Topic 3: Work and Energy Flashcards
What is work?
A measure of the energy transferred.
What is work measure in?
Joules (J)
What equation do you use to calculate work?
Work=force x distance
W=Fd
How can energy be lost?
Can be lost as heat to the surroundings by air resistance and friction.
What is gravitational potential energy?
The energy stored in an object as the result of its vertical piston or height.
What is the equation to work out gravitational potential energy?
Gravitational potential energy=mass x gravitational field strength x change in height
PE=mgh
What is kinetic energy?
Movement energy.
What is kinetic energy measured in?
Joules (J)
What do all moving objects have?
Kinetic energy.
What is the equation to calculate kinetic energy?
Kinetic energy=1/2 x mass x velocity ²
KE=1/2mv²
How do you calculate total energy?
Gravitational potential energy + kinetic energy=total energy
PE+KE
What is elastic energy?
When an object is stretched or squashed, it stores elastic potential energy. (When you stretch a spring)
What is extension directly proportional to?
Force applied.
What is the limits of proportionality?
When the spring will not return back to its original length if you take away the force.
What is the spring constant?
The stiffness of the spring.
What is the spring constant measured in?
Newtons per metre N/m
What is the equation to calculate the force of storing energy in springs?
Force=spring constant x extension
F=kx
How do you calculate elastic potential energy?
Elastic potential energy= 1/2 x spring constant x extension ²
Ee=0.5 x k x e²
How do you measure the work done stretching/compressing a spring?
The area under the force-extension graph.
What is Hooke’s law?
The extension of a spring is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.
How do you reduce aerodynamic losses?
more streamlined designs.
How do you reduce rolling resistance?
having correctly inflated tyres / using materials which don’t heat up as much as they are squashed.
What do stop- start systems reduce?
Idling losses.
How do you reduced inertial losses?
Lighter cars.
What is the equation used to describe hooks law?
F=kx
Force(N) = spring constant(N/m) x the extension(m)
When does Hooke’s equation not work?
When the elastic limit has been exceeded. (limit of proportionality)
When does Hooke’s equation not work?
When the elastic limit has been exceeded. (limit of proportionality)
When does Hooke’s equation not work?
When the elastic limit has been exceeded. (limit of proportionality)
when 5 things make fuel consumption more prominent?
Uphill Carrying large loads High speed Rough surfaces Under-inflated tyres
What are 3 car safety features?
Seat belts
airbags
crumple zones
In terms of work done, how do air bags and crumple zones reduce the force on the driver?
They increase the distance over which the energy is transferred.
In terms of momentum, how do air bags and crumple zones reduce the force on the driver?
Slow the car and passenger as gradually as possible; deceleration decreases (which will decrease the force).
How do seat belts work and what are they?
Strong belt of stretchy material.
Prevents the person being thrown forward in a crash and stretchy material absorbs some of the energy.
How do crumple zones work and what are they?
Section at front and back of the car designed to crumple on impact.
Slows car over longer period so it decreases the deceleration (which decreases the force).
How do air bags work and what are they?
Bag inflates rapidly in front of a person during crash.
Acts as a cushion. slows passenger over longer period, reduces deceleration and force.
Can energy be destroyed?
No it is always transferred from one form to another.
