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Buoyancy

Back

Buoyancy is the upward force that a fluid (like water) exerts on an object that is placed in it. This force makes objects feel lighter in water and can make them float. Example: A rubber duck floats in a bathtub because the water pushes up against it with a buoyant force that is stronger than the duck’s weight.

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Displacement

Back

Displacement happens when an object is placed in a fluid and pushes some of that fluid out of the way. The amount of fluid pushed out is equal to the volume of the object that’s underwater. Example: When you step into a full bathtub, the water spills over the edge. That spilled water is the amount you displaced with your body.

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Gravitational Force

Back

Gravitational force is the pull that Earth (or any object with mass) exerts on another object. This force gives objects weight and pulls them toward the ground. Example: When you drop a pencil, it falls to the floor because Earth's gravity pulls it down.

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Archimedes’ Principle

Back

Archimedes’ Principle states that the buoyant force on an object in a fluid is equal to the weight of the fluid the object displaces. Example: If a rock pushes 1 liter of water out of a container when dropped in, the water pushes back with a force equal to the weight of that 1 liter of water.

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Plimsoll Line

Back

The Plimsoll line is a line marked on the side of a ship that shows how much cargo it can safely carry without sinking too low in the water.

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Hydraulic Device

Back

A hydraulic device uses a liquid (usually oil or water) to transmit force from one place to another. Example: A car jack uses hydraulics to lift a car off the ground when you’re changing a tire.

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Pneumatic Device

Back

A pneumatic device uses compressed air or gas to transfer force. Example: A dentist’s drill uses air pressure to spin at high speeds and clean teeth.

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Pressure

Back

Pressure is the amount of force applied to a certain area. It’s measured as force divided by area. Example: When you push a thumbtack into a wall, the small point puts a lot of pressure on a small area, making it easier to pierce the wall.

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Pascal (Pa)

Back

A pascal is the unit used to measure pressure. One pascal is equal to one newton of force applied to one square meter of area. Example: A tire might be filled to 200,000 pascals (or 200 kilopascals) of air pressure to work properly.

Front

Pascal’s Law

Back

Pascal’s Law says that when pressure is applied to a fluid in a closed system, the pressure is transmitted equally in all directions. Example: When you squeeze one end of a sealed plastic ketchup packet, the ketchup shoots out the other end—because the pressure moved through the entire packet.