Energy: Forces Doing Work Flashcards
State the law of energy conservation
Energy can’t be created or destroyed (can only be transferred into different forms)
Describe the energy changes involved when a ball is thrown upwards and then returns to its starting position
- Upwards: KE is converted to GPE
- Peak: Maximum GPE, zero KE
- Downwards: GPE is converted to KE
State any changes in the total energy of a ball that is kicked, assuming that no external forces act
The total energy of the system remains constant due to the conservation of energy
Describe the energy changes that occur in a filament light-bulb
- Electrical energy is transferred into light and heat energy
- Light is a useful energy form, heat is waste energy
Describe the energy transfers for a bungee jumper
- When falling, the GPE is converted to KE of jumper
- As the cord tightens, KE is converted and stored as Elastic Potential Energy (EPE)
- At lowest point, the jumper’s initial GPE equals the EPE stored in the cord
Explain why a bungee jumper slows down once the cord begins to stretch
- Kinetic energy decreases since it is converted to elastic potential energy
- Since KE is proportional to (velocity)2, as KE decreases so does velocity
Describe the energy changes in a power station
- Heat energy released in the reaction heats water to make steam
- Steam moves the turbine, converting kinetic energy
- Kinetic energy turns the generator
- Electrical energy as the generator generates electricity
In what ways can the energy of a system be changed
- Through work done by forces
- Through electrical input
- Through heating
How can energy be changed through work done by forces
A force which moves an object (kinetic energy) causes work to be done over a distance
What equation is used to measure the work done on an object
Work done (J) = force (N) x distance (m) / W=Fd
Why do wasteful mechanical processes cause a rise in the temperature of the surroundings
They cause energy to be transferred by heating the surroundings
What is the equation for kinetic energy
E = 1/2mv2
What is the equation for gravity potential energy
E = mgh
What is the definition of power
The rate at which energy is transferred
State 2 equations for power
Power = energy transferred / time
Power = work done / time
