Class 9 Physics: Work and Energy
In physics, work is an energy transfer that occurs when a force has a component in the direction of displacement. Feeling tired is not by itself enough to show that work has been done on an object.
What to understand
- Describe the central idea in your own words.
- Use a model, observation or relationship to explain a changed example.
- Notice and correct the likely misconception in the worked reasoning.
When is work done?
For a constant force in the direction of motion, work can be calculated as force × displacement. If a force is perpendicular to displacement, it does no work in that direction. Energy is the capacity to cause change, and it can be transferred between forms.
Lifting a bag transfers energy to gravitational potential energy. A moving bicycle has kinetic energy; brakes transfer some of it to thermal energy in the brake surfaces and surroundings.
Try, explain and check
Trace energy changes when a ball rolls down a ramp and stops.
Show a reasoning prompt
A 50 N force moves an object 2 m. What work is done if the force is along the motion?
Show a reasoning prompt
Work is not the same as “trying hard”; direction and displacement matter.
Show a reasoning prompt
Next step
Write a three-sentence revision summary, then continue to the related resource. For extra practice, visit the resource library and choose a worksheet that matches the skill you need.