Water pushes up

The idea

The upward force applied by a liquid on an object placed in it is called upthrust or buoyant force; it depends on factors including the density of the liquid.

Bottle in water

An empty bottle with its lid closed tightly is pushed into water.

What do you feel?

• An upward push
• A sideways push
• Nothing

Push and let go

Press Push the bottle down. Then press Let go.

Up it comes

You felt an upward push, and the bottle bounced back to the surface. So water applies a force on the bottle in the upward direction. All liquids apply such a force.

The force applied by a liquid on an object in the upward direction is called upthrust or buoyant force. All liquids apply it. It depends on factors such as the density of the liquid.

Notes

The upward force a liquid applies on an object is upthrust, or buoyant force. All liquids apply it.

Check yourself

The upward force applied by a liquid on an object is called …

In which direction does the buoyant force act?

Which liquids apply an upward force on an object placed in them?

An empty closed bottle bounces back up when you let go because the water …

• friction. Friction acts along surfaces. The upward push of a liquid is upthrust.
• weight. Weight is the downward pull of the Earth.
• upthrust, or buoyant force — correct. Yes!
• Upward — correct. Yes!
• Downward. Downward is the direction of the Earth's pull.
• Sideways only. The buoyant force acts upward.
• Only water. All liquids apply a similar upward force.
• All liquids — correct. Yes!
• No liquid does. All liquids apply an upward force.
• pulls it down. The water pushes it up.
• sticks to it. The water applies an upward force on it.
• applies an upward force on it — correct. Yes!