Copy the following sentences and circle the correct word to explain the link between floating, sinking and density:
z A (less/more) dense material will float in a (less/more) dense liquid. z A (less/more) dense material will sink in a (less/more) dense liquid.
Using this knowledge and Fig. 17.7.2, make a list of materials that would float in sugar syrup.
Buoyancy Buoyancy is another factor that affects if an object will float.
We know that pressure in liquids increases with depth. The force as a result of this pressure is known as upthrust. If the upthrust is large enough, it will keep an object afloat, or buoyant.
Archimedes’ principle states that an object placed in water will feel an upthrust equal to the weight of the water it displaced.
Diver
Upthrust
Fig. 17.7.3 Upthrust in a liquid
Overflowing cup?
A glass is filled with ice and water to the top, as shown.
1. When the ice melts, which of the following things do you think will happen to the level of the water?
a. It will go down. b. It will stay the same. c. The glass will overflow.
2. Discuss the possible reasons for your answer with your lab partner. 3. Set up this investigation at home or in school.
4. Record your observations and explain why they did or did not match your predictions.
Why do boats float?
Using a basin of water and two equal masses of modelling clay, carry out a demonstration to explain why a boat floats on water. Make sure you have one sinking object for comparison.
