Archimedes' principle
The upward force equals the weight displaced.
A lighter mug
When you lift a mug out of a bucket of water, it feels lighter while it is still inside the water.
Why do you think this happens?
What this lesson covers
The idea
An object fully or partially immersed in a liquid experiences an upward force equal to the weight of liquid it displaces; it sinks if that weight is less than its own weight and floats if equal.
A lighter mug
When you lift a mug out of a bucket of water, it feels lighter while it is still inside the water.
Why do you think this happens?
- The water pushes it up
- The mug shrinks
- Gravity becomes weaker
Compare the weights
Pick an object and put it in the liquid. Compare the bars.
Weight of liquid displaced
The upward force on each object matched the weight of the liquid it pushed aside. The stone pushed aside less than its own weight and sank. The others pushed aside exactly their own weight and floated.
Archimedes' principle: an object fully or partially immersed in a liquid experiences an upward force equal to the weight of the liquid it displaces. If that weight is less than the weight of the object, it sinks. If it is equal, the object floats.
- Weight of liquid displaced | Object
- Less than the object's weight | Sinks
- Equal to the object's weight | Floats
Notes
Archimedes' principle: the upward force on an immersed object equals the weight of the liquid it displaces. Less than its weight: it sinks. Equal: it floats.
Check yourself
The upward force on an object in a liquid is equal to …
The liquid displaced by an object weighs less than the object. The object …
The liquid displaced by an object weighs as much as the object. The object …
Who discovered that an immersed object feels an upward force equal to the weight of liquid it displaces?
- the colour of the liquid. Colour has no part. It equals the weight of the liquid displaced.
- the weight of the liquid it displaces — correct. Yes!
- the size of the container. It equals the weight of the liquid the object displaces.
- floats. It floats when the weight displaced equals its own weight.
- rises. It sinks when the weight displaced is less than its weight.
- sinks — correct. Yes!
- floats — correct. Yes!
- sinks. It sinks only when the weight displaced is less.
- disappears. With equal weights it floats.
- Oersted. Oersted found that a current produces a magnetic field.
- Archimedes, a Greek scientist — correct. Yes!
- Volta. Volta is known for the first battery.