Lifting a bag, pushing a cart, using a lever — all involve work, energy, and simple machines that make the job easier.
In science, work is done when a force moves an object through a distance, in the direction of the force:
A force of 10 N moves an object 5 m. How much work is done?
Work = Force × distance = 10 × 5 = 50 J
Kinetic energy is the energy of motion. Potential energy is stored energy due to an object's position, such as height above the ground.
A 2 kg object moves at 4 m/s. Find its kinetic energy using KE = ½mv².
KE = ½ × 2 × 4² = ½ × 2 × 16 = 16 J
A 2 kg object is held 5 m above the ground (g=10 m/s²). Find its potential energy using PE = mgh.
PE = 2 × 10 × 5 = 100 J
Simple machines, like levers, pulleys, and inclined planes, make work easier by changing the size or direction of the force needed — though they don't reduce the total work done.
Why is it easier to push a heavy box up a ramp (inclined plane) than to lift it straight up?
The ramp lets you apply a smaller force over a longer distance, which makes the task feel easier — even though the total work done is about the same
1. A force of 20 N moves an object 3 m. Calculate the work done.
2. A 1 kg object moves at 6 m/s. Find its kinetic energy using KE=1/2mv^2.
3. A 3 kg object is at a height of 4 m (g=10 m/s^2). Find its potential energy using PE=mgh.
4. Name one example of a simple machine.
5. Does a simple machine reduce the total amount of work needed to do a task?