Force, Work, and Energy

A Today you'll learn

Understand the scientific definition of work (Work = Force × Distance).
Distinguish different forms of energy: kinetic, potential, electrical, and solar.
Explore clean renewable energy sources versus finite fossil fuels.

B Let's understand

In everyday life, reading or thinking is often called work, but in science, work is performed only when an applied force causes an object to move through a distance in the direction of the force (Work = Force × Distance). If you push against a solid brick wall and it does not move, scientifically no work is done. Energy is the capacity to do work. Energy takes many forms: Kinetic energy (energy of motion), Potential energy (stored energy due to position, like water behind a dam), Light, Heat, Sound, and Electrical energy. Energy can transform from one form to another, but cannot be created or destroyed (Law of Conservation of Energy). Renewable energy sources like solar, wind, and hydroelectric energy are sustainable and non-polluting.

C See it step by step

Example 1: Is work done when a student carries a heavy school bag while standing at a bus stop?

Step 1: Check scientific definition: Work = Force × Distance.
Step 2: The student applies an upward force to hold the bag.
Step 3: However, because the student is standing still, distance moved = 0.
Step 4: Work done = Force × 0 = 0. Scientifically, no work is performed.

Example 2: Trace the energy transformation in a hydroelectric power station.

Step 1: Water stored high up in a dam possesses Gravitational Potential Energy.
Step 2: As water cascades down pipes, it turns into Kinetic Energy.
Step 3: Rushing water spins turbines, converting kinetic energy into Mechanical Energy.
Step 4: Generators convert mechanical energy into Electrical Energy transmitted to homes.

D Your turn

Scientifically, work is done only when:

Look back at "Let's understand" above for a clue.

E Ready to practise?

Key idea 1

Scientific work requires a force to move an object over a distance (Work = Force × Distance).

Key idea 2

Kinetic energy is energy of motion; Potential energy is stored energy.

Key idea 3

Energy cannot be created or destroyed; it only changes form.

Solar

Solar, wind, and hydro are renewable; coal and petroleum are non-renewable fossil fuels.

Friction is a force that opposes motion

Friction is a force that opposes motion, generating heat energy.

Warm up

1. What two conditions must be satisfied for scientific work to be done?

2. Give an everyday example where force is applied but no scientific work occurs.

3. What type of energy is stored in water held behind a high dam?

Practise

4. What type of energy does a speeding cricket ball possess?

5. State the Law of Conservation of Energy in your own words.

6. Name two clean, renewable energy sources.

Challenge

7. What energy transformation takes place in a solar panel on a rooftop?

8. Why is petroleum called a non-renewable source of energy?

Download worksheet (PDF)

Question 1: What two conditions must be satisfied for scientific work to be done?

Answer: A force must be applied, and the object must move a distance in the direction of the force

Question 2: Give an everyday example where force is applied but no scientific work occurs.

Answer: Pushing against a stationary wall or holding a heavy suitcase without moving

Question 3: What type of energy is stored in water held behind a high dam?

Answer: Potential energy (gravitational potential energy)

Question 4: What type of energy does a speeding cricket ball possess?

Answer: Kinetic energy

Question 5: State the Law of Conservation of Energy in your own words.

Answer: Energy cannot be created or destroyed; it only changes from one form to another

Question 6: Name two clean, renewable energy sources.

Answer: Solar energy and wind energy (or hydro/geothermal energy)

Question 7: What energy transformation takes place in a solar panel on a rooftop?

Answer: Light energy from the Sun is transformed into electrical energy

Question 8: Why is petroleum called a non-renewable source of energy?

Answer: Because it takes millions of years to form and cannot be quickly replenished once exhausted