Force, Work, and Energy
1. What Is Force?
FORCE is a PUSH or a PULL that can change the state of motion of an object.
'You apply force when you OPEN a door (pull), CLOSE a book (push), or KICK a ball (push).'
Examples of Push:
- Pushing a swing.
- Pushing a shopping cart.
- Pushing a chair under the table.
Examples of Pull:
- Pulling a drawer open.
- Pulling a rope in tug-of-war.
- Pulling a bucket of water from a well.
'PUSH moves things AWAY from you. PULL brings things TOWARDS you.'
2. Effects of Force
Force can do SEVERAL things to an object:
| Effect of Force | Example |
|---|---|
| Move a stationary object | Pushing a book across a table |
| Stop a moving object | Catching a ball |
| Speed up a moving object | Pushing a bicycle while riding |
| Slow down a moving object | Applying brakes on a bicycle |
| Change direction of a moving object | Hitting a ball with a bat |
| Change shape of an object | Squeezing a sponge, stretching a rubber band |
'Force can start motion, stop motion, speed things up, slow things down, change direction — or even change the SHAPE of something!'
3. What Is Work?
In SCIENCE, WORK is done when a FORCE moves an object through a DISTANCE.
'In everyday life, studying is hard work. But in SCIENCE, studying is NOT work because you are not moving anything!'
When Is Work Done?
Work is done ONLY when:
- A FORCE is applied.
- The object MOVES in the direction of the force.
| Activity | Force Applied? | Object Moves? | Work Done? |
|---|---|---|---|
| Lifting a bag | Yes | Yes | YES |
| Pushing a wall | Yes | No | NO |
| Reading a book | No (muscles, but object doesn't move) | No | NO |
| Kicking a ball | Yes | Yes | YES |
4. Simple Machines
SIMPLE MACHINES make work EASIER by changing the amount or direction of force.
'Simple machines help us do work with LESS EFFORT. They are the BUILDING BLOCKS of all complex machines.'
5. Lever
A LEVER is a rigid bar that rotates around a FIXED point (called the FULCRUM).
'A seesaw is a LEVER. You push down on one end, and the other end goes UP!'
Parts of a Lever:
| Part | Description | Example on Seesaw |
|---|---|---|
| Fulcrum | The FIXED point | The middle support |
| Effort | The force you apply | Pushing down |
| Load | The object being moved | The person on the other end |
Examples of Levers:
- Seesaw
- Crowbar (to lift heavy objects)
- Scissors (two levers!)
- Bottle opener
6. Pulley
A PULLEY is a wheel with a GROOVE and a ROPE that runs through it.
'Think of a FLAG going up a flagpole. The rope goes through a wheel at the top — that is a PULLEY!'
How a Pulley Works:
- You PULL DOWN on the rope.
- The LOAD goes UP.
- A pulley CHANGES the DIRECTION of force — you pull down, the load goes up.
Examples of Pulleys:
- Flagpole
- Curtains (string pulls curtains open/closed)
- Crane (lifts heavy materials)
- Bucket from a well
7. Inclined Plane
An INCLINED PLANE is a SLANTED surface that connects a lower level to a higher level.
'A RAMP is an inclined plane. It is EASIER to push a heavy box up a ramp than to lift it straight up!'
How It Works:
- You apply LESS force over a LONGER distance.
- Lifting straight up = MORE force over SHORTER distance.
- Ramp = LESS force over LONGER distance.
Examples of Inclined Planes:
- Wheelchair ramp
- Slide at the playground
- Mountain roads (winding up slowly)
- Loading ramp on a truck
| Simple Machine | What It Does | Examples |
|---|---|---|
| Lever | Multiplies force | Seesaw, crowbar, scissors |
| Pulley | Changes direction of force | Flagpole, crane, curtains |
| Inclined Plane | Reduces force needed over longer distance | Ramp, slide, mountain road |
8. Energy
ENERGY is the ABILITY to do WORK.
'Everything that happens needs ENERGY. Running, reading, cooking, growing — all need energy!'
Sources of Energy:
Renewable Energy Sources (can be REUSED):
| Source | How It Works | Clean? |
|---|---|---|
| Sun (Solar) | Sunlight → electricity | YES |
| Wind | Wind → turns turbines → electricity | YES |
| Water (Hydro) | Flowing water → electricity | YES |
| Biomass | Plant/animal waste → fuel | Mostly |
Non-Renewable Energy Sources (will RUN OUT):
| Source | How It Works | Clean? |
|---|---|---|
| Coal | Burned → heat → electricity | NO (pollutes) |
| Oil (Petroleum) | Burned → fuel for vehicles | NO (pollutes) |
| Natural Gas | Burned → heat → electricity | NO (pollutes) |
Forms of Energy:
| Form | What It Is | Examples |
|---|---|---|
| Light | Energy that helps us SEE | Sun, bulb, torch |
| Heat | Energy that makes things WARM | Fire, sun, heater |
| Sound | Energy we HEAR | Bell, speech, music |
| Electrical | Energy from ELECTRICITY | Fans, lights, TV |
| Kinetic | Energy of MOTION | Running, wind, flowing water |
| Chemical | Energy stored in SUBSTANCES | Food, battery, fuel |
9. Common Mistakes
- Confusing work in science vs everyday life: 'In science, if you push a wall and nothing moves, NO WORK is done — even though you feel tired!'
- Thinking simple machines are NOT important: 'Simple machines are EVERYWHERE. A doorknob is a wheel and axle. Stairs are an inclined plane. Scissors are levers!'
- Believing energy can be created or destroyed: 'Energy CANNOT be created or destroyed. It only CHANGES from one form to another. The law of CONSERVATION OF ENERGY.'
- Thinking all energy sources are renewable: 'Coal, oil, and gas take MILLIONS of years to form. Once used, they are GONE. They are NON-RENEWABLE.'
10. Key Facts to Remember
- 'Force is a PUSH or a PULL.'
- 'Work (in science) = Force × Distance moved in the direction of force.'
- 'Simple machines make work EASIER — lever, pulley, inclined plane.'
- 'Energy is the ABILITY to DO WORK.'
- 'Renewable energy (sun, wind, water) can be REUSED. Non-renewable energy (coal, oil, gas) will RUN OUT.'
11. Self-Test
Q1: What is force? Give two examples of push and two of pull.
Q2: When is work done in science? Give an example.
Q3: Name three simple machines. Give one example of each.
Q4: How does an inclined plane make work easier?
Q5: What is the difference between renewable and non-renewable energy? Give two examples of each.
Q6: What type of simple machine is a SEE-SAW? Identify the fulcrum, effort, and load.
Q7: What is the pulley used for on a flagpole?
Q8: Name one renewable energy source that comes from the Sun.
Answers:
A1: Force is a push or a pull. Push: pushing a cart, pushing a door. Pull: pulling a drawer, pulling a rope. A2: Work is done when a force moves an object. Example: Lifting a bag. A3: Lever (seesaw), Pulley (crane), Inclined Plane (ramp). A4: It reduces the FORCE needed by increasing the DISTANCE over which the force is applied. A5: Renewable energy can be used again and again (solar, wind). Non-renewable energy will run out (coal, oil). A6: A LEVER. Fulcrum = the middle point. Effort = the person pushing down. Load = the person on the other side going up. A7: A pulley CHANGES the direction of force. You pull DOWN on the rope, and the flag goes UP. A8: Solar energy (sunlight converted to electricity or heat).
