1. 1: Pressure depends on density and depth
Pressure and Upthrust
1: Pressure depends on density and depth
2) P = h x p x g ?
3: Float / sink ?

2. Upthrust in Action Bubbles rising.
Pushing a ball down into water and letting go.
Raising an old canon in a shipwreck to the surface using balloons.
Jellyfish drifting in the ocean.
A diving gannet rises to the surface of the sea.
A balloon rises into the upper atmosphere

3. Using Upthrust

4. The Portuguese Man of War

5. The Force of Upthrust
Upthrust is a force in fluids which pushes in an upward direction.
If the upthrust force is greater than weight the object will ……
If the upthrust force is less than weight the object will …….
If the upthrust force is the same as the weight the object will stay put or float.

6. Measuring and Investigating Upthrust
Can you find out the upthrust force acting on different materials ?
Can you use and read a Newton meter accurately ?
Can you calculate upthrust and present your results clearly ?

7. Measuring Upthrust Material Weight in air (N) Weight in water (N)
Upthrust (N)
Jelly fish
Rock
Perspex
Metal Weights
Plastic Mammoth

8. Upthrust Analysis
1: What type of materials have the greatest upthrust force acting on them ?
2: How do you think upthrust is related to density ?
3: How could you work out the density of the materials you tested ?

9. Calculating Pressure at Depth
Pressure at Depth Equation:
Pressure due to column of liquid
= height x density x gravity
(m) (kg/m3) (N/kg)
= P = h x ρ x g
PRESSURE INCREASES WITH DEPTH

10. Gravitational field strength
Example Questions
1) Calculate the pressure due to water on a whale at depth m in the sea.
2) Calculate the depth of a whale if the water pressure on it is Pa.
Atmospheric pressure Pa
Density of sea water
1030 kg / m3
Density of fresh water
1000 kg / m3
Gravitational field strength
10 N/kg

11. Advanced Upthrust Calculations
Calculate difference in pressure between top and bottom surfaces if distance = 0.75 m.
This P difference produces a net upthrust force =
P difference x area.