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101 Cards in this Set
- Front
- Back
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What is the definition of power?
In mechanics, what are the two equations that can be used to calculate power? State what each part of the equation means. |
Energy transferred per second. p = Fv p is power F is driving force v is velocity p = W/t p is power W is energy transferred t is time. |
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What is a Scalar? Give an example of a scalar. Can scalars be negative? Explain why. |
Scalar - quantity with a size/magnitude only. E.g. speed Scalars can't be negative since they have no direction. |
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What is a Vector? Give 5 examples of Vectors. Can vectors be positive and negative? Why? |
Vector - quantity with size/magnitude AND direction. E.g. Displacement, Acceleration, Deceleration, Force, Momentum. Vectors can be +ve and -ve since vectors have a direction. One direction is +ve, and the opposite direction is -ve. |
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When working with vectors, what must you always do first? |
ALWAYS pick a direction to be positive when working with vectors. |
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Force is a vector.
If two force vectors are in the same direction, how do you find resultant force?
Find the resultant force of the forces in the image. |
Add them. |
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When resolving vectors going in opposite directions, how do you resolve those vectors? Find the resultant force of these vectors. |
Subtract them from each other. |
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When two vectors are at right angles from each other, how do you find the resultant force?
Find the resultant force of these vectors. |
At right angles, use Pythagoras to find hypotenuse. That's resultant force. |
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If two vectors aren't at right angles OR in opposite directions, how do you find the horizontal and vertical components of the resultant vector? How do you find the magnitude of the resultant vector? |
Resolve each vector into its horizontal and vertical components. Resolve the horizontal and vertical components, Then to find the magnitude, do Pythagoras to find the hypotenuse. That is the resultant vector. |
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Define Distance. |
Total length travelled in a journey |
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Define Displacement. |
Shortest distance between two points in a given direction. |
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Define Speed. |
Rate of change in distance covered. |
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Define velocity. |
Rate of change in displacement. |
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Define Acceleration. |
Rate of change in velocity. |
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If speed is constant, what is the equation for speed?
Give the units of each part. |
Speed = distance/time
s = d/t s is in m/s d is m t is s
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If velocity is constant, what is the equation for velocity? |
v = s/t Velocity = Displacement/time. |
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SUVAT are a set of equations that can be used to find displacement, initial velocity, final velocity, acceleration and time. Give all the SUVAT equations and state what each variable means. |
s is displacement u is initial velocity v is final velocity a is acceleration t is time. |
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What condition must be met to use SUVAT equations? |
Acceleration must be CONSTANT! |
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For a displacement - time graph, what is the gradient equal to? |
Gradient = velocity |
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For a velocity - time graph, what is the gradient equal to? What is the area under the graph equal to? |
Gradient = acceleration Area under graph = distance covered |
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For an acceleration - time graph, what is the area under the graph equal to? |
Area under graph = speed up to that time. |
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If an object is in equilibrium (not moving), the opposite horizontal and vertical forces acting on the object are... |
They are equal to each other. |
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If a force is acting at an angle on an object, how can you find the force's horizontal and vertical components? Resolve the force vector into its horizontal and vertical components. What is the magnitude of the weight of the object? |
Use SOHCAHTOA to find the horizontal and vertical components. Magnitude of weight = 2gN (g is 9.81) |
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What is the definition of Free Fall?
What is the value of earth's g (gravitational field strength)? |
When only the gravitational attractive force (weight) acts on the object and nothing else.
g = 9.81 N/kg |
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What is the equation to calculate the weight of an object? |
W = mg W is weight m is mass (kg) g is gravitational field strength (9.81 N/kg) |
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If an object is dropped from a given height, and air resistance is negligible, Is it's acceleration +ve or -ve? What is its acceleration? What is causing it to accelerate? |
Item dropped, acceleration +ve. Acceleration = +g Gravity is causing the object to accelerate. |
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If an object is thrown horizontally into the air then comes down, and air resistance is negligible, is it's acceleration positive or negative? What is it's acceleration? What happens to the sign of the direction? |
Acceleration -ve Acceleration = -g The sign goes from +ve to -ve (or -ve to +ve depending on which direction is +ve.) |
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What is a Projectile? |
An object where only the force of gravity is acting on it. |
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What is the relationship between the horizontal and vertical directions of a projectile? |
They are INDEPENDENT OF EACH OTHER (Horizontal velocity/components doesn't affect vertical velocity/components and vice versa) The only thing the horizontal and vertical component share is time. |
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Can you resolve velocity vectors at angles?
And can you use SUVAT for each component (horizontal and vertical component separately?) And find the SUVAT components for the vertical and horizontal component?
What do you usually use to find the different variable of the vertival and horizontal components separately? |
Yes (and you can only use SUVAT on both components if both the horizontal and vertical component have a constant acceleration.
Usually, the horizontal component has a constant speed and 0 acceleration, so use speed = distance/time for horizontal component if thats the case.)
Usually, use SUVAT for vertical component Use s = d/t for horizontal component. |
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In projectile motion, what is usually happening to the horizontal velocity and why? |
Horizontal velocity usually stays constant since air resistance is negligible in most questions AND gravity only affects the vertical component. |
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What are the 2 equations for resultant force? |
F = ma And F = Driving force - Resisitve force. |
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SUVAT Practice. Find the time of flight. |
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What is the name of Newton's 1st law of motion and what does it state? |
1) Law of inertia. An object stays at rest or travels at a constant velocity in a straight line until an external force acts on it. |
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What is the name of Newton's 2nd law of motion and what does it state? |
2) Law of acceleration. The acceleration of an object is directly proportional to the resultant force acting on it, and the acceleration is in the same direction as the resultant force. (F = ma OR F = rate of change in momentum) |
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What is the name of Newton's 3rd law of motion and what does it state? |
3) Law of Action and Reaction. When two objects interact, they exert equal and opposite forces onto each other. |
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This is a pulley. How can you find the direction the pulley turns and the force at which the pulley moves with? How do you find the acceleration at which the pulley moves with? |
1) find the weight of each object using W = mg 2) Whichever one has the bigger weight, the pulley will turn in that direction 3) To find the force at which the pulley moves with, do: Bigger weight - smaller weight. 4) To find acceleration at which the pulley turns, do: Resultant force = total mass of both objects x accell (F = ma) then solve for a. |
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This is a semi - pulley. The 2kg weight is being cancelled out by the table. Why? 1) How would you find the force at which the pulley turns if friction and air resistance is negligible? What if there was a resistive force (like friction?) 2) How would you find the acceleration at which the pulley turns with? |
The 2kg weight is being cancelled out by the table because of Newton's 3rd law. The table is exerting an equal and opposite force on the object (2g). 1) To find the force at which the pulley turns (resultant), find the weight of the object that ISN'T on the table. Use W = mg. (If there is a frictional force acting between the table and the object on the table, subtract that frictional force from the weight of the object not on the table to get resultant force (force at which the pulley turns.) 2) To find the acceleration at which the pulley turns, do F = ma m is mass of BOTH objects F is resultant force Solve for a. |
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This is an object on an inclined plane. Label every force of relevance in algebraic terms. Assuming there's no air resistance and friction. Let the mass of the object be m kg. |
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Inclined planes may involve pulleys. Label every force of relevance. Let M2 = n for the sake of the answer. |
R = mgcos(Theta) |
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With ALL pulley situations, what do the two objects have in common? Under what circumstance does this hold true? |
The two objects move with the same acceleration AS LONG AS the string is taut (fully stretched) |
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When resolving forces, particularly with pulleys on inclined planes, do the opposite forces need to be on the same plane/orientation at all positions for you to be able to resolve them? Give an example using the diagram. |
Not necessarily (since technically the opposite force could be on the same plane all the way to another orientation.) E.g. ng and mgsin(Theta) can be subtracted from each other since they are in opposite directions. One is pulling the pulley down the slope and the other is pulling the pulley up the slope and over the edge of the slope. |
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When a mass is attached to a string and the string is made taut by the mass, the string experiences tension. In the diagram above, the string is pulling the object up. What is the equation for resultant force in this situation? (Using the weight of the mass and tension of the string)? |
T - W = ma T is subtracted by W since the weight is smaller than the tension due to the string pulling the mass up |
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A string will have tension if its taut. Pulleys have tension. When looking for tension, how many of the masses do you need to look at? When looking at x number of object/s, what is the equation for the resultant force x object/s is experiencing If: 1) the object/s weight is above the tension? (Object is falling) 2) the object/s weight is below the tension? (Object is rising) |
Only need to look at one object. 1) W - T = ma 2)T - W = ma |
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In all pulley types, if the string is taut, do both objects experience the same tension? |
Yes. |
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Sketch an Air resistance against Velocity graph. What is the relationship between air resistance and velocity in terms of proportionality? If velocity increases, what will happen to air resistance. |
Graph starts at 0. R is directly proportional to V². If V↑, R↑.
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Define terminal velocity. |
The velocity at which driving forces equal resistive forces. |
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If a person jumps from a plane, explain how the person will reach terminal velocity. |
1) Person jumps out of plane, essentially released from rest
2) The force of weight makes the person accelerate downwards. As the velocity rises, air resistance rise 3) Eventually, air resistance equals weight, and the person stops accelerating. They reach terminal velocity.
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Terminal velocity can be reached in cars. Draw a car, label the direction of the driving force and state what we call the driving force for a car Label the direction of the resistive force and give 3 examples of resistive forces to a car. Label the direction of the car's acceleration as well. |
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In free fall, weight is a driving force. For cars, engine thrust is a driving force. What is the difference between engine thrust and weight? |
Weight is a fixed force, Whilst Engine thrust can be changed by pressing on the pedal. |
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In free fall, what are the two ways to increase terminal velocity? Explain how each method increases terminal velocity. |
1) increase the weight of the object by increasing its mass. If there is more weight, more air resistance is needed to reach terminal Velocity. The object accelerates for longer, so terminal velocity will reach a greater value. 2) Reduce cross-sectional area. There will be less area for air resistance to occur on. It will take longer to reach terminal velocity since the object accelerates for longer. Terminal velocity will be greater. |
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What are the 3 ways that you can increase terminal velocity in cars? |
1) Increase driving force (Engine thrust) 2) Reduce mass (so less friction will occur, meaning the resistive forces will be less) 3) Reduce cross-sectional area (Less air resistance) |
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Define momentum. (Its equation) |
Mass x velocity. |
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A change in resultant force does what to momentum (and rate of change in momentum) ? |
Leads to a change in momentum and rate of change in momentum. |
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If resultant force were to rise, what will happen to momentum? |
F↑, p↑ |
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What does the conservation of momentum state? Write an equation that represents the conservation of momentum. |
Momentum before an event = momentum after an event AS LONG AS no external force is applied to the system. (m1u1 + m2u2 = m1v1 + m2v2) |
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Write the symbolic equation for momentum. Give the units of each component. |
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Is momentum a vector? Why? Can momentum be +ve or -ve? What does this depend on? |
Yes. p = mv. Since velocity is a vector, momentum is a vector as well. Momentum can be +ve or -ve. This depends on which direction is taken as +ve and whether velocity is +ve or not. |
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What is the definition of Impulse? What are the 2 equations for impulse? Give the units of each component. |
Impulse - Change in momentum. V is final velocity U is initial velocity. |
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Don't know how to make this a question, but its info that must be known. NOTE: In physics, variables can have different units. See if those units can equal the standard one that you know is used for the variable by multiplying or dividing dirrerent parts by changing the symbols. This must usually be done in multiple choice only. |
Teet |
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What is the equation for Rate of change in momentum? What is the unit for rate of change in momentum? What do rate of change in momentum and force have in common? |
Rate of change in momentum and force have the SAME UNITS. |
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When finding velocity using conservation of momentum, what must you do regarding direction? |
Choose which direction is +ve and -ve and state what direction the velocity is in. |
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What is the equation for Kinetic Energy? |
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What are the 2 types of collisions? |
Elastic Inelastic |
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What is an Elastic Collision? |
A collision where kinetic energy is not lost |
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What is an Inelastic collision? |
Collision where the colliding objects have less kinetic energy after the collision than before the collision. |
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Draw a visual demonstration of an elastic collision using a bouncy ball hitting the ground. |
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Is energy a scalar or a vector? (This includes ALL energy, including kinetic) When is energy +ve and -ve? |
Energy is a SCALAR. It only has magnitude, NO direction. If energy is gained it's +ve If energy is lost it's -ve. |
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Draw a visual demonstration of an inelastic collision. Label every part of relevance. How would you find the fraction of kinetic energy lost? How would you convert this fraction to a percentage? |
To convert fraction to percentage, x100. |
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In elastic collisions:
1) Is total momentum conserved?
2) Is total energy conserved?
3) Is total kinetic energy conserved? |
1) Yes
2) Yes
3) Yes |
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In inelastic collisions: 1) Is total momentum conserved? 2) Is total energy conserved? 3) Is total kinetic energy conserved? |
1) Yes
2) Yes
3) No |
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In explosions, objects usually start at rest, then an explosion causes the objects to move away from each other. Does the conservation of momentum still apply? |
YES |
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In an explosion, what is the initial velocity of both objects if they are still? Look at the image. When an explosion occurs, the conservation of momentum can be applied. Which object will gain a greater speed and why? |
Initial velocity = 0 The 10kg mass will gain a greater speed since its lighter. |
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In a real explosion, multiple pieces fly in opposite directions. Why does the conservation of momentum still apply for many pieces flying in many directions? Draw a diagram that demonstrates this. |
For pieces flying in opposite directions, momentum before = momentum after. Think of them as independent situations |
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1) Where do explosions occur in nuclear physics? 2) Can you approach this situation as a normal explosion in terms of momentum? |
1) Nuclear decay 2) Yes. |
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This is about car safety. What is thinking distance? What is the equation for thinking distance? |
Distance travelled by a vehicle during the driver's reaction time. Reaction time is in seconds. |
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What is Braking distance? What is the equation for braking distance? |
Distance travelled by the vehicle when the breaks are applied. |
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What is Stopping distance? What is the equation to find stopping distance? |
Stopping distance = thinking distance + braking distance. |
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What factor affects Thinking distance? What causes this factor to be reduced? If this factor reduces, what happens to thinking distance? What causes this factor to be increased? If this factor increases, what happens to braking distance? |
.Driver's reaction time (Reduced if they've taken stimulants, like coffee) Reaction time ↓, thinking 'd' ↑ thinking 'd' ↑ (Increased if they've taken depressants, like alcohol) Reaction time ↑, thinking 'd' ↑. |
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What factors increase braking distance? What factors decrease braking distance? |
Braking distance increased by: Worn tyres Oily, wet, icy roads Braking distance decreased by: Dry roads, good condition tyres. |
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In an inelastic collision, Kinetic energy can be converted to different forms. Give 2 examples of energy types that kinetic energy can be converted to in an inelastic collision. |
Thermal, Sound. |
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What does the conservation of energy state? |
Energy can't be created or destroyed. It can only be transferred to different forms (Other energy types). |
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What is the unit of energy? |
Joules (J) |
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What is the definition of 1 Joule? |
The energy needed to raise a 1N weight through a vertical height of 1m. |
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What is the definition of work done? What is the equation for work done? |
Work done - The transferring of energy from one place to another using force. W = F x d Work done = force x distance Work done (J) Force (N) Distance (m) |
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What is the equation for work done by gravity (Also known as potential energy)? |
Ep = m x g x h m is mass (kg) g is grav field strength 9.81(N/kg) h is vertical height (m) |
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When gravity is the only force acting on an object, and air resistance is negligible, what equation can be used? |
Decrease in Ep = Increase in Ek |
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What does the area under a force against distance graph equal? |
Area under force against distance graph = work done. |
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When a force other than gravity (usually friction or air resistance) is acting on an object, and the object is traveling at an angle, what is work done equal to? |
Work done = Ek lost - Ep gained |
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For an object moving horizontally, what is work done equal to? (Besides F x d?) Give the word and symbol equation. |
Work done = Change in Ek. W = ½mv² - ½mu² |
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Define Power. What are the 2 equations for power in mechanics? What are the 2 possible units for power? |
The rate of doing work. Power units are W (Watts) or J/s (Joules per second) |
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What is the definition of 1 Watt? |
The transfer of 1 joule per second. |
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What is the definition of moment? (Its equation). Give the symbol equation for moment as well. And the units of the different variables. |
Force x perpendicular distance from the line of action of the force to the pivot. Moment = F x d Moment unit is Nm Force is N d is m |
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Draw a visual example of moments with a wrench spinning around a bolt. |
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What does the principle of moments state? |
When a system is in equilibrium, Total clockwise moments = Total anticlockwise moments (around a given pivot) |
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If you have a given force, And you move it further away from the pivot, will it produce a greater moment or smaller moment? |
It will produce a greater moment. |
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If an object is being balanced by a pivot, must the weight of the object being balanced be considered as well when calculating moments? |
Yes. |
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Cant put into question NOTE: Pivot types can vary. They may be points of balance, or points that bar-like objects are hung from. It an object is on top of a pivot, the pivot will have a reaction force on the object, and that force must be considered when resolving forces but NOT with moments, unless there are 2 or more pivots then consider the reaction force from the pivot/s you aren't taking moments about when calculating moments about a pivot. If the object is being hung from a string/s, tension will be in the string. Consider tension when calculating moments and resolving forces unless you are taking moments about one point where the object is hung from, then ignore that tension for moments since it's on the pivot, meaning it's 0 distance from the pivot. BUT consider it when resolving forces. |
Teet |
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In moments, forces may be applied at angles. How would you find the moment created by that force? |
Resolve that force into it's horizontal and vertical components using SOHCAHTOA, then use the component that is perpendicular to the pivot to find the moment created by that force. |
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What is a Couple? Draw a visual example of a couple acting around a pivot. |
A pair of equal and opposite forces acting on a body. |
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Explain how couples work. Give all the details you can about couples. Mainly:
What do the two forces in a couple have in common? What is different about them? What is the total moment created by a couple?) |
Forces are equal, but are on opposite sides of the pivot at the same distance from the pivot. They are moving in the same direction, and produce equal moments. So the total moment they produce is the moment of one x2. Total couple moment = 2(F x d) |
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Define Centre of Mass. |
The point on an object where it's weight acts. |
