Work, Energy, and Simple Machines
Class 9 · Science
3 ideas in Class 9 Science, explained in plain words, with games and quizzes to practise.
Work and its Direction
Part of: Work and its Direction
In science, a force does work when it causes displacement along its direction. Work is zero if there is no displacement or if the force is perpendicular to the motion.
Why it matters. This meaning of work helps explain how pushes and pulls transfer energy.
Try it in two minutes
- Push a toy along a table.
- Notice the direction of your push and its movement.
- Hold a bag still and compare that with moving it.
Try at home. Think about the direction of a force when you carry an object across a room.
Energy and Power
Part of: Energy and Power
Energy is the capacity to do work. Work on an object changes its energy, while power tells how quickly work is done.
Why it matters. Energy ideas connect motion, height, heat, light and sound. Power lets us compare the rate of doing a task.
Try it in two minutes
- Lift a light object a short distance.
- Notice the effort used and the height reached.
- Repeat the lift more quickly and compare the rate of doing work.
Try at home. Look for energy changing form when an appliance is used.
Mechanical Energy and Simple Machines
Part of: Mechanical Energy and Simple Machines
Kinetic energy comes from motion; potential energy can be stored because of position or shape. Simple machines such as ramps and levers make tasks more convenient by changing how effort is applied.
Why it matters. These ideas help explain why objects speed up as they descend and why a longer ramp can reduce the push needed.
Try it in two minutes
- Roll a toy car down a shallow ramp.
- Compare it with lifting the car to the same height.
- Use a ruler balanced on a pencil to lift a small eraser.
Try at home. Notice ramps, levers and pulleys used around your home or school.
What your child will practise
- Energy and Power: Jungle Quick Fire (Quick Fire)
- Energy and Power: Lab Explorer Quest (Collect the Answer)
- Energy and Power: Space Puzzle (Clue Puzzle)
- Mechanical Energy and Simple Machines: Mission Control Sort (Sort It Out)
- Work and its Direction: Desert Quick Fire (Quick Fire)
- Quiz: Energy and Power (8 questions)
- Quiz: Mechanical Energy and Simple Machines (8 questions)
- Quiz: Work and its Direction (8 questions)