3 Work, energy and momentum Flashcards
What are the 9 forms of energy?
light thermal kinetic chemical nuclear gravitational potential elastic potential sound electrical (magnetic)
What is work?
An object is said to have work done when it transfers energy
How do you work out work done?
Work done (joules,J) = force (newtons,N) + distance (metres,M)
What is power?
The amount of work done in a given time
How do you work out power?
Power (watts,W) = work done (joules,J)
——————————
time (seconds,S)
Where is work done to overcome friction mainly transferred?
As energy that heats the objects that rub together and the surroundings
Where is gravitational potential energy present?
In any object that is raised above the ground
What does gravitational potential energy depend on?
Weight
How far ‘it’ moves vertically
When does GPE increase/decrease?
Increase - when the object moves up
Decrease - when the object moves down (towards floor)
How do you work out weight?
Mass (kg) x gravity (N/kg)
How do you work out work due?
force x distance moved
How do you work out change of GPE (J)?
mass (kg) x gravitational field strength (N/kg) x change of height (m)
(weight (N) x change of height (m))
What does kinetic energy depend on?
Mass
Speed
How do you work out kinetic energy (J)?
1/2 x mass (kg) x speed/velocity2(squared) (m/s2)
How do you work out momentum? (kgm/s)
mass (kg) x velocity (m/s)
What does the law of conservation of momentum state?
In a closed system, the total momentum before an event and the total momentum after an event are the same/equal
What is speed in a certain direction?
velocity
What are external forces?
a change in momentum
What is force?
the rate of change of momentum
What happens when 2 objects push each other apart?
- they move apart with different speeds if they have different masses
- they move apart with equal and opposite momentum so their total momentum is 0
When vehicles collide what does the force of impact depend on?
Mass
Change of velocity
Duration of impact
Complete this statement:
The longer the impact time is…
the more the impact force is reduced
What happens when 2 vehicles collide?
- they exert equal and opposite forces on each other
- their total momentum is unchanged
How do seat belts and air bags increase car safety?
Spread the force across the chest and also increases the impact time reducing the force
How do side impact bars and crumple zones improve car safety?
they give way in an impact and therefore increase the impact time
How can we use the conservation of momentum in car crashes?
To find out the speed of a car before impact
