Transcript Why Things Float - Noadswood Science

Why Do Things Float? What
Would You Say?

D. Crowley,
Why Things Float
L.O: To understand why objects float
Floating
 Look at the model boat below - how is it floating?
 See if you can identify the forces involved, and add the force
arrows (what size should these arrows be)?
 In your book draw a diagram of the boat, add the force arrows
and add a short explanation of why it floats.
Floaters
 So why is it some objects float, and others sink?
 Look at the picture below of some rocks sinking. Explain why
the rocks sink
Reaction Force - up thrust of water
This time the reaction force
is much smaller than that of
gravity - this means that the
rock will accelerate into the
depths…
Gravity
Experiment
 So far we have found that some objects float, and others sink
 There must be a pattern to which ones float, and which sink can you work it out?
 Is it that all heavy objects sink, and all light ones float? Does it
depend on the size and shape of an object? Steel sinks, yet we
make boats out of steel! How is this possible?
Experiment
 You have been provided with different objects, all weighing the
same, but of different sizes
 See if you can predict which will float, and which will sink
 Write down your predictions, and your reasons for this
Results
Object
10g mass
10g of rock
10g of wood
10g of wax
10g of rubber bung
Prediction
Sink / Float
Result
Sink / Float
Density
 The reason some objects float and others sink is due to density
 Density is an equation of an object’s mass divided by its volume
Density = mass / volume
 If an object is more dense than water, it sinks
 If it is less dense, it floats
Steel versus Steel Boat
100kg
Steel
100kg Steel
Steel boat = less dense than water  floats
Steel bar = more dense than water  sinks
How Do Life Jackets Work?