*Go get the physics book with the soccer ball on it. Name ______
Chapter 5
1. Define energy:
The ability to do work
2. Review … what is work? Why is energy measured in the same units as work?
Work is a force applied a given distance, it takes energy to do work. There is a direct connection between work and energy
3. What are the five main forms of energy, how does it work (definition?) and give one example.
1. Mechanical Energy – The energy associated with motion
· Ex. Water in a waterfall, a car travelling at 50 mph
2. Chemical Energy – Energy required to bond atoms together, released when bonds are broken.
· Ex. Fuel in a rocket has stored chemical energy. Converts to heat energy when the fuel is burned.
· Starting a fire releases chemical energy in the form of heat.
· Playing a sport uses the chemical energy stored in your muscles obtained from food.
3. Heat Energy – The internal motion of atoms. The faster the molecules move, the more heat energy is produced.
· Ex. Friction converts mechanical energy to heat energy. i.e. rubbing hands together
· Heat energy causes ice cream to melt and drip down your hands
4. Electromagnetic Energy – Energy produced by moving electric charges
· Ex. Power lines carry electromagnetic energy into your home in the form of electricity
· Electric Motors are driven by electromagnetic energy
· Light – each color represents a different amount of electromagnetic energy
· Also carried by X-rays, radio waves and laser light
5. Nuclear Energy – Heat and light energy released when the nucleus of an atom splits or fuses with another is nuclear energy, nuclear energy is the most concentrated form of energy
· Ex. Sun’s energy is from fusion reaction between Hydrogen and Helium
4. It is energy you must pay for on your electric bill. Electric companies usually express the total amount of energy used in kilowatt-hours (kWh) – the flow of 1 kilowatt of electricity for 1 hour. How many joules of energy do you get when you pay for 1 kWh? (1 joule = 1 watt x 1 second; 1 kW = 1000 watts; 1 hour = 3600 seconds).
1 kw*h x 3600 seconds x 1000 watts x 1 joule = 3,600,000 Joules
1 hr 1 kw 1 watt* 1 second
5. What is kinetic energy? Give three examples.
Kinetic energy is the energy of motion.
· Ex. Truck whose brakes are out,
· rubber-band flying through the air,
· bowling ball rolling towards your foot
6. What is the mathematical equation for kinetic energy?
K.E. = mass x velocity2
2
7. Which of the two factors in the numerator will have a greater effect on kinetic energy? Why?
- (Use the table on the bottom of page 113 to help you if you need to)
The velocity because it is squared and thus the effect on KE due to velocity is exponential
8. When does a skier have more kinetic energy, when skiing downhill or cross-country? Explain.
A downhill skier will have more kinetic energy because gravity acts as a force on the skier causing the velocity to increase more than when skiing cross-country.
9. What is potential energy? Give three examples.
Potential energy is the energy of position.
· Ex. Stretched rubber band
· Skier at the top of a hill
· Piano on the ledge of a skyscraper roof
10. What is an energy conversion?
Changes in the forms of energy
11. Please come up with two examples of kinetic-potential energy conversions.
Tossing a ball in the air
Playing Ski-ball
Rollercoaster
12. Answer the five questions in the “Activity: Thinking” box on page 117.
1. Highest potential energy is at the highest point on the rollercoaster track
2. Car has the greatest KE when the velocity is the greatest, so probably at the lowest point
3. Least potential energy when car is at the lowest point on the track and the KE is highest
4. Car has more potential energy at the highest point, point E
5. At point A the potential energy is the highest and the kinetic energy is lowest because the car is not moving yet. As the coaster approaches point B the potential energy reaches its lowest, and the kinetic energy is at its maximum. As the car approaches point C, the potential increases and the Kinetic decreases somewhat. As the car approaches point D, Potential decreases some while Kinetic increases a bit. Finally, as the car approaches point E, potential is increased as Kinetic energy decreases slightly with the uphill travels.
13. Name an example of something that uses each conversion.
- Electrical energy to heat energy – Space heater
- Mechanical energy to heat energy – Running energy
- Chemical energy to heat energy – battery powered curling iron (converts to electromagnetic first)
- Chemical energy to mechanical energy – battery operated remote control helicopter
14. Why do light bulbs get hot when they’ve been for awhile?
Some of the electromagnetic energy is lost as heat energy when the bulb converts electromagnetic energy to light energy.
15. State the Law of Conservation of Energy
Energy can neither be created or destroyed by ordinary means, but only converted from one form to another. Energy conversions occur without a loss or gain in energy.
16. How is energy related to speed?
You travel at a faster speed when you run, than when you walk and it takes more energy to run than it does to walk.
17. How is energy related to force?
A force is required to change motion. A force acting on an object does work. When a force does work on an object it changes the energy of the object.
18. How is energy related to power?
Power is the rate at which work is done. Thus power is the rate at which energy is consumed.
19. Apply the Law of Conservation of energy to work being done on a machine.
Work that comes out of a machine can never be greater than the work that a machine puts out. When you do work on a machine you transfer energy to the machine. Energy is conserved, thus work is conserved.
20. Sound is produced by vibrations in a medium such as air. The particles are first pushed together and then pulled apart. Why is sound considered a form of mechanical energy?
The particles are in motion and that is what causes sound – because of the motion it is mechanical energy.
21. Water is boiled. The resulting steam is blown against huge turbine blades. The turning blades spin in a magnetic field, producing electricity. Describe in order the energy conservations.
· Water boiled – Chemical to heat energy
· Steam moves turbines – heat to mechanical energy
· Turbines move in magnetic field to produce energy – mechanical to electromagnetic energy