Year 9 Science · Unit 3 · Lesson 2
Foundation Worksheet
Learning Goals
Fill the gap
Choose the correct word from the word bank. Each word is used once. Two words will not be used.
The law of of energy states that energy cannot be or destroyed. A group of objects that we study together is called a . In a system, energy cannot enter or leave, so the total energy stays constant. When energy seems to disappear, it has really spread into the surroundings as . Scientists say that every joule of energy can be for. Energy that does not do the job we want is called energy.
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
A closed system can create extra energy if a big enough force is applied.
Correct it:
Energy that is “lost” as heat has been transformed into thermal energy that spreads into the surroundings. It still exists.
Correct it:
Conservation of energy means that nothing in the universe ever moves or changes.
Correct it:
An open system lets energy enter and leave, so the total energy inside it can change.
Correct it:
No real machine can be 100% efficient, because some energy always becomes waste thermal energy.
Correct it:
1. A spinning top slows down, wobbles and falls over. Where has its kinetic energy gone? Explain using the law of conservation of energy.
2. A pot of water boils on a stove with no lid. Is the pot and the water an open system or a closed system? Give two pieces of evidence.
Data: energy accounts for three devices
A class measured the energy going into three devices, and the useful energy and waste energy coming out. Each row shows one device running for a few seconds.
| Device | Energy in (J) | Useful energy out (J) | Waste energy out (J) |
|---|---|---|---|
| Radio | 40 | 8 (sound) | |
| Blender | 500 | ? (kinetic energy of the blades) | 175 |
| Electric toothbrush | 12 (kinetic energy of the brush) | 18 |
Source: sample class results.
3. Use energy in = useful energy out + waste energy out to find the three missing values in Table 1. Show your working.
Radio waste J
Blender useful J
Toothbrush energy in J
4. Which device in Table 1 wasted the greatest fraction of its energy? Show how you worked it out.
5. A child on a playground swing is given one push and then left alone. Each swing is a little lower than the one before, until the swing stops. Explain where the energy goes, using the law of conservation of energy.