Work, Energy And Momentum Flashcards
What is the unit of both work and energy?
Joule, J
What is the energy transferred equal to?
Work done
What is work done to overcome friction transferred as?
Energy that heats the objects that rub together and the surroundings
What doe the gravitational potential energy of an object depend on?
It depends on its weight and how far it moves vertically
What is gravitational potential energy?
Energy stored in an object because of its position in the earths gravitational field.
What happens in terms of gravitational potential energy when an object is moved vertically?
It gains gravitational potential energy equal to the work done on it by the lifting force
What is the change in gravitational potential energy measured in?
Joules
What is gravitational field strength measured in?
N/kg
What is power?
The rate of transfer of energy
What does the kinetic energy of an object depend on?
Depends on the mass and speed of the object
The greater the mass and the faster the speed of an object…
The more kinetic energy it has
If an elastic band is stretched and then released what energy transfer occurs?
Elastic potential to kinetic energy
What do all moving objects have?
Momentum
What factors affect momentum?
Velocity
Mass
The greater each of them are the greater the momentum
What is the unit of momentum?
Kgm/s also writes an Ns
Whenever objects interact, the total momentum before the interaction is…
Equal to the momentum afterwards, provided no external forces act on them
What happens in terms of momentum when objects interact provided no external forces act on them?
Momentum is conserved or the overall change in momentum is zero
What does momentum have?
Size and direction
When two objects are at rest what is their momentum?
Zero
In an explosion what do the objects do to each other in terms of momentum?
They move apart with equal and opposite momentum, one momentum is positive and one is negative so the total momentum after the explosion is zero
What happens when a force acts on an object that is able to move or is moving?
It changes momentum
When vehicles collide what does the force of impact depend on?
Mass
Change in velocity
Duration of the impact
For a particular change in momentum the longer the time taken for the change…
The smaller the force that acts
In a collision the momentum of an object…
Often becomes zero during the impact- the object comes to rest
If the impact time is short…
The forces on the object are large, as the impact time increases the forces become less
What are crumple zones?
They are in cars and are designed to fold in a collision. This increases the impact time and so reduces the force on the car and the people in it
What is impact time?
Time taken for a collision to take place
What is the total momentum after an explosion equal to?
The total momentum before the explosion
Two student on roller skates stand holding each other in the playground they push each other away. What can you say about the momentum of each student?
It is equal and opposite
Why do cars have crumple zones at both the front and rear of the car?
The car could be hit from either the front or rear, in either case the crumple Zones reduce the forces on the car and increase impact time
Crumple zones and side impact bars reduce the forces acting by…
Increasing the time taken to change the momentum of the car
How do air bags reduce the forces on the occupants of the car in a collision?
They sleep read the forces across the body, if a drivers heads hits an airbag it changes momentum slowly so the forces on the head are less than it would be if it changed momentum quickly by hitting the steering wheel
How do seat belts reduce the forces on the occupants of the car in a collision?
They stop the wearer being flung forward if the car stops suddenly, the seat belt stretches slightly increasing impact time and reducing the force
When a force moves an object move what is done?
Energy is transferred and work is done
What is work done to overcome friction transferred as?
Heat that is transferred to the surroundings
