Understanding Forces: Contact and Non-Contact

Forces

• A force is any push or pull that causes an object to move.
• If an object is moving, an outside force must have acted on the object to get it moving.

Pushing Force

• Occurs when something moves away from you.
• An example of this is pushing a child on a swing.

Pulling Force

• Occurs when something moves closer to you.
• Example is playing tug-of-war.

Contact Forces

• Contact forces involve direct contact to move an object.
• Examples include objects moved by the wind or someone kicking a soccer ball.

Non-Contact Forces

• A non-contact force acts on an object without touching it.
• Examples include gravitational, electrostatic, and magnetic forces.
• Non-contact forces have acted on an object if it moves without being touched.

Gravity

• A common non-contact force that pulls objects to Earth's center.
• Keeps everyone grounded.
• When throwing a ball into the air, gravity force is stronger than yours, which makes the ball come back down.

Mass and Weight

• Weight is based on gravity and measures the force of gravity pulling down on an object
• Weight measures how hard gravity pulls an object toward Earth's surface.
• A person would weigh less on the moon due to the moon's gravitational pull being weaker.
• If someone weighs one hundred pounds on Earth, they would weigh 16 pounds on the Moon.

Magnetism

• An invisible force where magnets either attract each other or repel.
• Happens when objects are made of a magnetic material.
• Magnetic materials are metals like iron, nickel, and cobalt.
• A magnet pulls or pushes objects made from magnetic materials.
• Magnets have a north and south pole.
• Opposite poles attract; like poles repel.
• Magnetism is used to stick things on a fridge.

Maglev Cars

• Maglev is short for "Magnetic Levitation".
• Cars float above the track instead of rolling on wheels.
• They work because two like poles of a magnet repel each other.
• Magnets are on the bottom of the cars; the tracks have magnets, too., with same poles facing each other.
• Repulsion lifts the car above the track, making it float.
• Maglev cars may have a smooth ride since they are not in contact with the track.

Hard Drives

• Hard drives use magnetism to store data.
• Contains a round piece called a disk, which is able to be magnetized.
• Disk is circles with millions of tiny spots on it. Each spot can be a '1' or a '0' called binary code
• There is a little arm called the read/write head in which hovers above the disk.
• Head has a tiny magnet.
• Hard drive stores information on a round piece called a disk.

Static Electricity

• Occurs when electrical charges move from one object to another.
• Like rubbing hair against a balloon.
• The negative charges in her hair move to the balloon causing more negative charges in the ballon.
• Extra negative charges on the balloon create a buildup of negative charges.
• Shaking hands can produce a shock due to static electricity as electric charges jump from one person to another.

Dangers of Static Electricity

• Static electricity can attract dust to computer monitors or TV screens.
• It can cause clothes to cling.
• Anti-static sprays, liquids, and clothes prevent the build-up of charge.
• Lightning is the most dangerous example of static electricity.
• Lightning is caused when static electricity builds up in clouds which then causes a spark that forms between the ground and the clouds. Touching a live wire with a large electric charge can cause an electric shock.

Electrostatic Force

• Everything is made up of tiny microscopic particles that can have an electrical charge, either positive or negative.
• If two of the same particles touch, they pull away from one another.
• Opposite charges attract (pull towards) each other.
• Charged particles move, this is called an electrostatic force.

Lightning

• An electrostatic current that travels from one electrically charged object to another.
• In clouds, raindrops bump into each other causing a static electric charge.
• If a thundercloud is negatively charged at the bottom, the positively charged objects on Earth's surface become drawn to the cloud and creates lightning.

Photocopiers

• Photocopiers use static electricity to copy images.
• Inside the photocopier is a drum that gets a positive charge hit with light.
• Areas where light bounces back lose their charge.
• Toner (powder) has an opposite charge to the drum, and sticks to the charged parts.
• Paper is given a stronger charge, so toner jumps from the drum to the page.
• Paper is then heated up, and toner sticks.