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Learning that some forces can move objects without even touching them.
Have you ever seen a paperclip 'jump' toward a magnet before they even touch? It looks like a magic trick, but it is actually a secret superpower of the universe!
A force is simply a push or a pull. Most of the time, we use contact forces. This means we have to touch something to move it. When you kick a soccer ball, your foot touches the ball. When you pull a wagon, your hand touches the handle. But did you know some forces can move things without touching them at all? These are called non-contact forces. They work like invisible hands reaching through the air!
Quick Check
If you push a swing with your hands, is that a contact force or a non-contact force?
Answer
It is a contact force because your hands are touching the swing.
Why does your pencil always fall to the floor when it rolls off your desk? Why doesn't it float up to the ceiling? The answer is gravity. Gravity is an invisible force that pulls all objects toward each other. Because the Earth is so massive, its gravity is very strong. It pulls everything 'down' toward the center of the planet. Gravity is a non-contact force because it pulls on you even when you are jumping high in the air and not touching the ground!
1. Hold a feather in your left hand and a ball in your right hand. 2. Open both hands at the same time. 3. Even though they fall at different speeds, gravity pulls both of them down to the floor. You don't have to push them; the invisible force of gravity does the work for you!
Quick Check
Does gravity push things away from Earth or pull them toward Earth?
Answer
Gravity pulls things toward Earth.
Magnets are another example of an invisible force. Every magnet has a magnetic field around it. This is a space where the magnet can pull on certain metals like iron. Magnets have two ends called poles: a North pole () and a South pole (). These poles can do two things: attract (pull together) or repel (push away). They can do this through paper, plastic, and even water without ever touching the object!
1. Take two magnets and try to touch the North () pole of one to the North () pole of the other. 2. You will feel an invisible 'cushion' pushing them apart. 3. This is the force of repulsion. You are feeling a force even though the magnets aren't touching!
1. Hang a magnet from a string. 2. Hold a paperclip just below it so it 'hovers' in the air without touching the magnet. 3. Gravity is pulling the paperclip down, but the magnetic force is pulling it up. Because the forces are fighting, the paperclip stays still in mid-air!
Which of these is a non-contact force?
What happens when two North () poles of magnets are put together?
True or False: Gravity only works on heavy objects like bowling balls.
Review Tomorrow
Tomorrow morning, try to name one thing you did that used a contact force and one thing that used a non-contact force.
Practice Activity
Find a refrigerator magnet and see if it can pull a paperclip through a piece of paper or a thin plastic ruler!