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129 Cards in this Set
- Front
- Back
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What is Order of Magnitude?
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the relative size of the number in powers of ten
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How do you find order of magnitude?
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log functions
ex. the order of magnitude of 5600: log5600=3.74, order of magnitude is 10^4 without a calculator, compare the number (in scientific notation) to 3.16. if greater or equal, add one to the exponenet for the order of magnitude ex. 5.6 x 10^3 5.6>3.16, therefore the order of magnitude is 10^4 |
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What are fundamental units?
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units whose quantities are the most basic value (m, kg, s, A, K, mol, candela)
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What are derived units?
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units involving 2 or more fundamental units combined mathematically
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How do you choose the number of significant figures in the answer?
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the answer should not be more precise than the least precise factor in the calculation
ex. 4.732 - 3.62 = 1.112 = 1.11 |
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What is a random error?
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an error due to the natural fluctuations in data (not all pennies have the same mass). Reduce these errors by having a large sample size and conducting multiple trials
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What is a systematic error?
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error due to poor experimental design
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Contrast precision and accuracy
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Accuracy is how close a value is to an accepted result. Precision is the range of your reported values.
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What number of significant digits should uncertainty have?
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The significance of error should aggree with the significance of the reported value.
ex. 256 +/- 40 is wrong 260 +/- 40 is correct |
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How do you calculate uncertainty?
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When adding/subtracting add the relative uncertainties. When multiplying/dividing add the percentage uncertainties.
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What is relative uncertainty?
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absolute uncertainty/measurement
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What is percentage uncertainty?
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relative uncertainty x 100%
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What type of function should all graphs be plotted as?
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linear. y = mx + b
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How do you make graphs linear?
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to manipuluate y = x^2 into y = mx + b, take the square root of the y value
ex. displacement vs time is y=x^2 graph squareroot(displacement) vs time to manipulate y = 1/x into y = mx + b, plot as 1/x ex. pressure vs volume looks like y=1/x. plot pressure vs 1/volume y=kx^n, plot logy=logk + nlogx y=ke^(cx), plot lny=lnk + cx |
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Contrast displacement and distance traveled
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Displacement is net distance from starting point to ending point. Distance traveled is the length of the path taken
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On a graph that plots velocity vs. time, how do you find the total displacement?
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the area under the curve
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What is the derivative of velocity?
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acceleration
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At terminal velocity, how does the frictional force compare to weight?
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frictional forces and weight are equal
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Are horizontal and veritcal components of any vector dependent or independent of each other?
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independent (the x part of the motion would occur exactly as it would if the y part did not occur at all). called perpendicular independence
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What is projectile motion?
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projectile motion occurs when an object moves simultaneously in the x and y directions
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What are projectiles?
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objects that have been launched into the air
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What is a trajectory?
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the path a projectile will follow
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What is range?
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the horizontal distance traveled by a projectile
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In projectile motion, what is the acceleration?
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acceleration in the y direction is -9.8m/s^2
acceleration in the x direction is 0 if air resistance is ignored |
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What is the acceleration when an object is launched horizontally?
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acceleration in the x direction is 0
initial acceleration in the y direction is 0 (the object initially moves only in the horizontal direction) |
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Contrast speed and velocity
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speed is a scalar, velocity is a vector (it has direcion)
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A person is throwing rocks horizontally off a bridge. If the rocks are thrown faster, how will that affect the time it takes to strike the ground and how will it affect the range?
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the time won't be affected, but the range will increase
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A plane is moving horizontally and drops a crate of food several meters before a village. When the food lands in the village, where will the plane be?
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above the village (remember perpendicular independence)
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An object has been launched at an angle. What is the velocity at the peak of the trajectory?
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the y velocity is zero
the x velocity is the same as when the projectile was launched |
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When objects are launched at an angle, what shape is the trajectory?
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upside-down "U". symmetrical
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At what angle is a maximum range produced?
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45 degrees
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When are identical ranges produced (with respect to their angles)?
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when the angles are symmetrical about 45 degrees
ex. 70 and 20 |
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If you shot your gun straight up while riding in a convertible at constant velocity, where would the bullet land?
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in the barrel of the gun
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Can velocities be relative?
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yes. observers in different frames of reference may measure different values for an object in motion. in most cases our reference frame is that of the ground
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A cannon fires a cannon ball horizontally from a clif. If the height of the clif is doubled, what happens to the range?
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range is squareroot(2) times as much
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What is a force?
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vector quantity that is defined as a push or pull
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contrast contact forces and fields
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contact forces exist if there is physical contact between 2 objects
fields exert their force over a distance |
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What is inertial mass?
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the property of a body that resists change in motion (Newton defined mass as the quantity of matter)
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What is Newton's First Law of Motion?
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If the net force acting on a body is zero, the object will move with constant velocity. This law is only valid in an intertial reference frame (such as Earth)
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Contrast a state of rest and constant velocity
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they are equivalent because they don't require a net force to maintain
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What is Newton's Second Law of Motion?
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The acceleration of an object is the ratio of the net force acting on the body to its mass. Sum(F)= ma
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What direction does acceleration point in?
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the direction of the net force
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What is a newton?
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force unit. (1kg)(1m/s^2)= 1 N
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What is a Free Body Diagram?
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vector diagram that represents the object and the forces acting on it
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What is Newton's Third Law of Motion?
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When one body exerts a force on a second body, the second body exerts equal but opposite force on the first body. Forces always come in pairs. Fab = -Fba
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Why do you lunge forward when your car suddenly stops?
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Newton's 1st Law. your constant velocity hasnt been interrupted but the car's has
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The 2nd Law states that when a net force acts on an object it must accelerate. Suppose that two forces simultaneously act on an object. Can you conclude that the object accelerates at a greater rate?
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yes, but only if the forces are applied in the same direction
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Is a net force applied to an object that falls at a constant speed? At constant acceleration?
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no net force at a constant speed. there is a net force at constant acceleration
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If you crash into a car, which object experiences the greater force of impact? The greater acceleration?
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the forces of impact are equal. the car experiences the greater acceleration
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What is Newton's Law of Universal Gravitation?
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every particle in the universe exerts an attractive force on every other particle
F = GMm/r^2 |
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What is the universal gravitational constant?
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G = 6.67 x 10^-11 Nm^2/kg^2
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Contrast weight and mass
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Weight is the gravitational force exerted by Earth on an object's mass. Mass is resistance to acceleration
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A moon rover will weigh 6 times more on Earth. In an experiment on Earth, a force of 1000N is required to produce a horizontal acceleration of 1.5 m/s^2. What force will be needed to produce the same acceleration on the moon?
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same forces needed (mass/inertia doesn't change)
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What is normal force?
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the force that a surface exerts on an object that is resting upon it. It always actings perpendicular to the surface. N = -W
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What is apparent weight?
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weight as measured in a non-inertial (accelerating) reference frame. To find, use Sum(F) = ma
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Do you feel heavier in an elevator that accelerates up or down?
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upward. N > W (to move up), N > mg
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What is your apparent weight at free fall?
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0, there is no normal force so you feel weightless
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What is friction?
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a force that acts parallel to the surface and opposes the motion of the object. it arises when contact points betwen the surface and object are rough (welds)
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What is static friction?
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force that keeps an object a rest
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What is kinetic friction?
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friction once an object is in motion. kinetic friction values are generally less than static friction. if the applied force is equal to the kinetic friction, constant velocity occurs.
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Which creates more friction: sliding a book across a surface on the edge or the cover?
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neither, the friction is the same
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If you are moving a sled at constant velocity, would it be easier to push or pull the sled (assuming the angles are equal)?
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pull, there is less friction (you decrease the normal force by pulling upward too)
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What is tension?
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when a force is aplied to one end of a rope, it is applied to an object at the other end
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What direction is tension in?
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always away from the object and in direction of rope
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What does it mean to be in equilibrium?
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an object in equilibrium has zero acceleration (may be moving at constant velocity)
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A circus performer hangs from a rope. Is the tension in the rope greater when the performer is accelerating upward (climbing) or hanging?
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accelerating upward. accelerationg means Sum(F) does not equal zero. T>W
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A boat in still water is given a horizontal push to get it moving. It gradual slows down. Describe the force acting on the boat as it slows.
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there is a backward force that diminishes with time
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What is linear momentum?
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Momentum is a vector quantity that is dependent upon mass and velocity. p=mv. it is in kgm/s
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What is Newton's Second Law and Momentum?
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Sum(F) = delta(p)/delta(t). the rate of change of the momentum of a particle is proportional to the net force acting on the particle and is in the direction of the force
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What is the impulse-momentum theorem?
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A force applied during some duration of time (impulse) produces a change in momentum. the term F delta(t) is called the impulse, represented by J. Fdelta(t)=delta(p)
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Why is "follow through" important in sports?
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it increases the impact time, which increases the change in momentum
ex. without follow through Fdelta(t)=delta(p) (100)(.1)=10 with follow through (100)(.2)=20 |
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Can a system of two objects have a total kinetic energy that is non-zero but have a total momentum that is zero?
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yes. KE is never negative so two KEs can't add up to be zero but momentum can
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A baseball and a water balloon have the same mass. The water balloon explodes when it hits you, but the baseball bounces off. Why is the baseball more painful?
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the baseball has low impact time, so it has more force. the change in momentum is also greater
Fdelta(t)=delta(p)=mdelta(v) baseball: m(-10-10)=-20m balloon: m(0-10)=-10m |
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What is the Law of Conservation of Linear Momentum?
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the total linear momentum of any closed, isolated system does not change
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What are internal forces?
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forces that objects within a system exert on each other
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What are external forces?
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forces exerted on objects that are not a direct result of the objects within the system (gravity, friction, air resistance). when there are no external forces, the system is isolated
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Superman hovers in midair, grabs Lex Luther, and throws him forward. After the toss Superman remains in the same spot. Why is this incorrect?
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po=0=pf
MsVs + MlVl can only equal zero if Vs is negative, therefore Superman must move backwards |
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What are elastic collisions?
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collisions where KE and momentum are conserved. the objects hit and fly apart
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What are inelastic collisions?
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the initial KE is converted (deformation energy, sound) but momentum is conserved. objecty may stick together
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Are the x and y components of momentum conserved separetely?
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yes because of perpendicular independence
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What is the Center of Mass?
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center of gravity; point where a body's weight can be considered to be concentrated
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What happens to the motion of the center of mass during an explosion?
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it does not change
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When is an object stable?
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when the center of mass is between the lower extremes of the base
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A rocket is fired vertically. At its highest point it explodes. What happens to the total momentum and the total kinetic energy?
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the total momentum is unchanged but the total kinetic energy increases (velocity is squared so its never negative)
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In a graph that plots delta(p) vs. delta(t), how do you find the force?
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the slope
Fdelta(t)=delta(p) F=delta(p)/delta(t) |
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In a graph that plots force vs. delta(t), how do you find the impulse?
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the area under the curve
impulse=Fdelta(t) |
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A truck collides with a bicycle. Which will undergo a larger change in momentum?
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neither, they both have the same change in momentum
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A constant force of F is applied to a ball of mass, m. the ball changes its speed from v1 to v2. What is the impulse?
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m(v2-v1)
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What is work?
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the product of force and the displacement caused by that force
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If a force is applied and the object does not move, is work done?
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no
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How does work affect Kinetic Energy?
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work results in a change in KE. if you do work on an object it must move, so it acquires a velocity
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What is the Work Energy Theorem?
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the net work done on an object by the net force acting on it is equal to the change in kinetic energy. W=KEf-KEo
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If net work is positive, will the object speed up, slow down, or remain the same?
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speed up (and increase KE)
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Is it possible for the same object to have different velocities at two different times but have the same KE each time?
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yes, forward/backward
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Is it possible for a slow moving car to have more KE than a fast moving motorcycle?
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yes, mass
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A shopping bag is hanging straight down from your hand as you walk across the floor at constant velocity. Does the bag's handle do any work on the bag? What if you ride up an escalator at constant velocity? Constant acceleration?
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no-perpendicular independence
yes- vertical displacement (no net work) yes-change in velocity (net work) |
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How do you resolve weight vectors on an inclined plane?
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Wparallel=Wsinθ
Wperpendicular=Wcosθ |
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What is potential energy?
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energy that an object has due to its position in space because gravity has the ability to do work on that object
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Does horizontal motion matter for potential energy?
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no, delta(h) is independent of path
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When does gravity do positive work?
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when the object is falling
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When is a force conservative?
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when it does no net work on an object that travels in a closed path, thus starting and finishing at the same point (ex. gravity)
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What is a non-conservative force?
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the work done on an object depends on the path taken (ex. friction). KE will be gained or lost, there will be a difference in speed
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What is power?
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power is the amount of work done in a measured amount of time (rate). In Watts (1 Watt = 1 J/s)
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What is the Principle of Conservation of Energy?
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energy can be converted but never created or destroyed
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When a force is not constant, how can you find the work done?
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W=(Fcosθ)s is not valid
find the area under the curve for a graph of Fcosθ vs. s |
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What is uniform circular motion?
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an object travels in a circular trajectory at a constant speed
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What is a period (T)?
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the time needed to complete one revolution
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What directions do the velocity and acceleration point?
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velocity is always tangent to the circle
acceleration points toward the center of the circle |
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Is velocity constant in uniform circular motion?
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no because the direction is always changing
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A car goes around a curve. Can it be in equilibrium?
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no because it is accelerating
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What is a centripetal force?
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force that produces centripetal acceleration; whatever force keeps the object moving in a circle
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A trapeze artist is holding his partner with his legs over the bar and his arms hanging down. Is it harder for him to hold his partner when she is hanging straight down or when she is swinging through a circular arc?
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hanging- the tension in his arms equals her weight
when she is swinging there must be a centripetal force also Farms>weight |
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A child is riding a merry-go-round. Will the child be more likely to fly off the ride if he is near the edge or the middle?
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edge. he covers more distance in the same amount of time so he is moving faster. he needs more force to stay in the circle
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What keeps a satellite in orbit?
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gravitational force as a cetnripetal force
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How many possible speeds can a satellite orbit while remaining at the same distance from Earth?
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one. v= squareroot(GMe/r)
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Is the orbit speed independent of the mass of the satellite?
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yes. v = squareroot(GMe/r)
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How can you produce artificial gravity on a satellite?
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by rotating the satellite.
Without rotation, all bodies within the orbiting object cannot push against each other (all falling/accelerating towards center of circle) so there is no normal force. An astronaut must be in contact with the satellite's walls to feel the artificial gravity |
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On a banked curb, what does the normal force do?
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A component of the normal force provides the centripetal force and a compenent counters the weight (so it doesn't slip)
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Is vertical circular motion uniform?
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no, the speed changes because of gravity
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Why is there a minimum speed for vertical circular motion?
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if the speed is too slow at the top of the circle, the rider will lose contact with the track (and normal force provides some of the centripetal force)
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What is gravitational field strength?
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force per unit mass; acceleration due to gravity at that point
I=GM/r^2 |
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What is gravitational potential energy?
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potential energy at any level
U=-GMm/R |
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What is gravitational potential?
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energy per unit
V=-GM/R |
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Define and derive escape speed
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initial velocity needed to leave a planet's gravitational pul
Eo=Ef KEo + PEo = KEf + PEf 1/2mv^2 + -GMm/r = 0 + 0 v=squareroot(2GM/r) |
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Define and derive Kepler's Third Law
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law of periods, a^3/p^2 = C (a is the semimajor axis)
-GMm/r^2 = mv^2/r v=2pir/T -GM/r=4pi^2r^2/T^2 r^3/T^2 = -GM/pi^2 |
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Derive the total energy of a satellite
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-GMm/r + 1/2mv^2
find v: GMm/r^2=mv^2/r -GMm/r + 1/2 MGm/r -1/2GMm-r |
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As an object gets further from the Earth, what happens to its gravitational potetential energy?
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increases towards zero
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What are Kepler's 1st and 2nd laws?
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1st: planets have elliptical orbits and the sun is the focal point
2nd: planets move faster when closer to the sun |
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The order of magnitude for a quantity of X is 10^4. The order of magnitude for quantity Y is 10^12. What is the ratio of Y to X?
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10^8
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