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8
F = ma = 4 × 2.
Class 6 · Bangla Version · General science
Forces, energy and electricity
Connect forces, energy transfers and a simple electrical model.
Shared cross-level core and stretch unit. Start with the core questions, then use the stretch example for deeper work. The same unit is available in related class and board pathways; it is not a full grade-specific or examination-specification course. A teacher should select the appropriate depth and further topics.
Learn the idea
A resultant force changes velocity; balanced forces do not require an object to be at rest. Energy is transferred between stores or to the surroundings. Electric current is charge flow in a complete circuit. A battery transfers energy to charges; current is not used up by a lamp in a simple series circuit.
Worked example
A 2 kg trolley accelerating at 3 m/s² needs a resultant force of 6 N. A 6 V supply driving 0.5 A transfers 3 J each second, because power P = VI = 3 W.
- Name the system and forces.
- Choose an equation with consistent units.
- Explain the direction of transfer or change.
Stretch example
A 100 W device running for 30 s transfers E = Pt = 3,000 J. If 2,100 J is useful output, efficiency = 2100/3000 = 0.7 or 70% for that defined useful output.
Your written practice
Show your working on paper and enter your answer here. If it does not match, compare the model and try again.
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12
P = VI.
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circuit
Current needs a complete path in this model.
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Yes. It can move at constant velocity with zero resultant force.
Do not confuse motion with acceleration.
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Some transferred electrical energy becomes thermal energy in the lamp and surroundings.
Describe an energy transfer rather than energy disappearing.
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300
E = 20 × 15.
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Different purposes classify different transfers as useful, changing the numerator.
Explain what the ratio compares.
Paper energy audit
Draw an energy-transfer diagram for a fictional battery-powered lamp.
Review with a guardian or teacher
- Label the input and outputs.
- Account for total energy.
- Use paper or a simulator; never mains electricity.
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