Topic 8: Energy- Forces Doing Work Flashcards
What’s the law of energy conservation?
Energy cannot be created or destroyed -it can only be transferred into different forms
What are 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
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 the lowest point, jumper’s initial GPE equals the EPE stored in the cord
Explain why a bungee jumper slows down once the cord begins to stretch?
- KE decreases since it’s converted to EPE
- 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 KE
- KE 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 forces?
A force which moves an object (KE) causes work to be done over a distance
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’s the definition of power?
The rate at which energy is transferred (or rate at which work is done)
What’s the unit of power?
Watt (W)
What is one watt equivalent to?
1 joule per second (J/s)
What does a power rating of 10W mean for an electrical device?
It converts 10 Joules of energy every second
What is efficiency?
The proportion of energy that is converted usually, rather than wasted/ dissipated
