Force And Energy Notes, Quizzes & Revision

Force and Energy

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Notes suitable for learners aged age_replace (Kenyan context).

1. What is Force?

Force is a push or a pull that can change an object's motion or shape. Forces have both size (magnitude) and direction — they are vectors.

• Unit: Newton (N). 1 N = 1 kg · m/s².
• Common examples: pushing a door, gravity pulling an apple, friction slowing a bicycle.

2. Types of Forces (short list)

• Gravity: attraction between masses (keeps us on Earth).
• Friction: force that resists motion between surfaces.
• Normal force: support force from a surface (e.g., floor supports you).
• Tension: pull in ropes or strings.
• Applied force: any push or pull by a person or machine.

3. What is Energy?

Energy is the ability to do work or cause change. Energy comes in many forms and can be transformed from one form to another.

• Unit: Joule (J).
• Common forms: kinetic, potential (gravitational), thermal (heat), chemical, electrical, light.

4. Key Energy Forms and Simple Formulas

• Kinetic energy (moving object): KE = 1/2 m v² (m in kg, v in m/s). Example: A 1 kg stone moving at 4 m/s: KE = 0.5 × 1 × 16 = 8 J.
• Gravitational potential energy: PE = m g h (g ≈ 9.8 m/s²). Example: 2 kg on a 3 m high shelf: PE = 2 × 9.8 × 3 ≈ 58.8 J.
• Work done by a force: W = F × d (force along direction of motion × distance). Unit: J.
• Power (rate of doing work): P = energy / time. Unit: Watt (W) where 1 W = 1 J/s.

5. Conservation of Energy (simple explanation)

Energy cannot be created or destroyed — it only changes form. For example, when water falls at a hydroelectric dam, gravitational potential energy becomes kinetic energy and then electrical energy at the turbines. Some energy becomes heat due to friction.

6. Kenyan context — energy examples

• Geothermal (Olkaria): heat from the Earth → electrical energy.
• Hydropower (Tana River and others): falling water → turbine rotation → electricity.
• Wind (Lake Turkana): moving air → turbine rotation → electricity.
• Solar: sunlight → electrical energy via solar panels (common for rural electrification).

These local examples help learners see energy transformations in real Kenyan projects.

7. Simple visual: Falling object (PE → KE)

8. Common classroom calculations (step-by-step)

1. Find PE at top: PE = m g h.
2. If object falls (no friction), KE at bottom = initial PE.
3. Use KE = 1/2 m v² to find speed v: v = sqrt(2 g h).

9. Key vocabulary (quick)

Force, Newton (N), Mass, Acceleration, Energy, Joule (J), Work, Power, Kinetic energy, Potential energy, Conservation of energy, Friction.

10. Quick checks (practice)

• What is the unit of energy?
• Calculate the work done when a 10 N force moves a box 3 m along the floor (W = Fd).
• State one local Kenyan example where potential energy is converted to electrical energy.

Notes prepared for: subject_replace — adapt examples and numerical difficulty for learners aged age_replace.