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43 Cards in this Set

  • Front
  • Back
Basics understanding of energy
Energy is the capacity of a system to do work or to make some kind of change. Whenever there is a change in a system, energy is involved
Kinetic Energy
Kinetic energy is the energy an object when it is in motion. Equation
What should you think when you see an object in motion?
The kinetic energy the object has
The momentum that object has
The conservation of energy if applicable
Potential Energy
The energy of an object with a certain mass with respect to a certain force acting on that mass. This can be gravitational potential energy where the force is gravity or chemical potential energy where the force is the energy between the bonds.
First Law of Thermodynamics
This law states that energy is neither created or destroyed in a system. Energy is only transferred from one system to another
Total Mechanical Energy
This is the total mechanical energy of a system. This equation states that the total mechanical energy of system is the sum of the KINETIC and POTENTIAL ENERGY of that system.
What is the exception for the equation of total mechanical energy?
The exception is that this equation does not account for heat lost in a system due to frictional forces.
Example of a non conservative force
Friction since it results in the non conservation of energy
Example of conservative force
Gravity and electrostatic energy
Two ways to tell is a forces is conservative
1) if the work needed to move an object is the same regardless of the path taken by that object
2) If the net work done an object to move it in a round trip is 0
What will the work be in a non conservative system?
Work, where there are non conservative forces at play, will be the difference between the potential energy and the kinetic energy.
What will the work be in a conservative system?
Work will always be 0 in a conservative system. This means that there will be a direct proportionality between kinetic energy and potential energy: as one goes up, the other goes down.
Work
A process by which energy is transferred from one system to another
What is unit for work?
Joule
What are the two ways energy is transferred from one system to another?
Work and heat
Calculating Work
Equation
If you have a block on an inclined plane, how would you calculate the force needed to push a block up the plane?
You would find the angle that the plane makes with the floor and simply multiply that by mg. You should have the equation mgsin(x). Since we are using the x direction and the angle that the ramp makes with the floor, we are going to use the sin function
Power
The rate at which energy is transferred from one system to another. Equation
Unites for power
the units of power are Watts (W)
Work Energy Theorem
This states that the total work of a system can be calculated by the difference between the the INITIAL KINETIC ENERGY and the FINAL KINETIC ENERGY.
Momentum
Equation
Inertia
The tendency of objects to resist changes in their movement
Impulse
Impulse is the change in an objects momentum. It is the difference between the initial momentum and the final momentum
If you multiply force by the time that that force was acting upon an object, what will you get?
Force times the time that that force was acting on that object will be change in that objects momentum. This means that Ft= mv(I) - mv(F)
When you see a collision on an mcat, what should you be thinking?
You should be thinking of momentum
Three types of collisions tested
1) Fully Elastic
2) Inelastic
3) Fully Inelastic
How does the fact that the equation for conservation of momentum deals with vectors affect the signs used in the equation?
Since the equation deals with vectors and vectors have magnitude and direction you need to establish the positive and negative direction for the collision. You set this up.
What is the difference between inelastic collisions and fully inelastic collisions?
Inelastic collisions is similar to what we find in real life in that the initial kinetic energy will be greater than the final kinetic energy. What this equation tells us is that some of the energy is given off as heat or light. Fully inelastic collisions do not take energy dissipated into account, for these types of problems the masses of the final object will be summed together.
Fully elastic collisions
In this type of collision there is a full conservation of momentum and kinetic energy
Inelastic Collisions
In this type of collisions the initial kinetic energy is greater than the final kinetic energy since some of the energy is given off as heat
Fully inelastic collisions
In these types of collisions, the objects involved will stick together and the masses will be summed.
In what type of collisions will energy be lost?
In inelastic collisions, there will be a loss of energy since some of the kinetic energy will be converted to heat and lost.
Mechanical Advantage
This is the idea that you can reduce the amount of force you put on a system and still get the same amount of work just by increasing the distance over which you exert that smaller force. The equation for work is W=F d cos (x). Just by looking at the equation you can tell that if W is kept constant and F is decreased, d would have to increase.
Mechanical advantage of an inclined plane
The mechanical advantage of an inclined plane is that you can decrease the force to achieve a certain displacement by simply increasing the distance.
Distance vs Displacement vis a vis mechanical advantage
When you have a mechanical advantage, the displacement is being kept constant while the distance through which that displacement is being achieved is being increased which thus decreases the force needed to achieve the desired displacement
If you have a block hanging from a ceiling bu two ropes, what will the tension be in those two ropes?
The tension will be equal to the total force being suspended. In other words, if the total force of the object being suspended is represented by mg (from the equation F=ma) then the tension (T) in both ropes will be T (1) + T (2) = mg
What is the tension on a rope in a pulley system?
The tension on the rope in a pulley system depends on how many ropes there are in the system. If there are 2, ropes, then the tension will be equivalent to half the force pulling downward. If there are 6 ropes, the tension in each rope will be (mg)/6 (the total force pulling down divided by 6 ropes)
What happens as you add more pulleys to a pulley system?
The overall efficiency will go down.
In a pulley system, how is the distance that A ROPE needs to be pulled related to the DISPLACEMENT of the object itself?
The more sets of rope you have, the less force you need to exert on the pulley but the greater the distance you need to pull on the rope. Meaning, if you have two ropes in the pulley system and a object that needs to be raised 3 meters, then you need to pull the rope a distance of 6 meters. If you have an object that needs to be moved 3 meters, and you have 6 ropes, you need to pull the rope 18 meters
Efficiency
Equation
E=(Load x Load Distance)/(Effort x Effort Distance). What does each mean?
Load = mg of the object.
Load Distance = How much you need to move the object.
Effort = how much energy (J) you need to put in.
Effort Distance = The length of the rope through which that effort needs to be applied
Center of Mass
The point at which the entire force due to gravity can be though as acting.
Center of mass of a three dimensional object
The center of mass of a three dimensional object will be give by three coordinates. In terms of the equation, the mass is remain the same but the only difference will be the value of the X,Y,Z coordinate.