1. Lots of slides, but little writing…
Pressure and Buoyancy
Lots of slides, but little writing…

2. Pressure - how a force is spread over an area.
Pressure- a measure of how much force is acting on a certain area.
Pascals (Pa)- the measure of pressure. 1 pascal is the pressure of 1 newton of force over 1 square meter.
Pressure = (N/m2)

4. Pressure acts in all directions in a fluid.
Fluids are made of a large number of small particles all of which are moving in all directions and bumping into each other.
Each bump causes a force.
An object in a fluid gets bumped by the particles from every angle.

5. Fluid pressure depends on density and depth.
Think about it… the more stuff (density) you have pushing on you, the more pressure.
Also, the deeper you go under the water (depth), there is more water pushing down on you from above. More pushing = more pressure.

6. Water Pressure and Depth
QUESTION #1
Which tube of water would push against your hand the hardest? Why?

7. Water Pressure and Depth
Water pressure is determined by depth.
The deeper you go, the more water above you to push against you.

8. Pressure and Density
Density is a measure of how much stuff (matter) a substance has by volume.
Air is less dense than water. (Air floats on water)
Therefore, Air has less matter (stuff) in it by volume.
Therefore an equal volume of air exerts less pressure than an equal volume of water.
There is less matter (particles) to push against you.

9. Air Pressure and Elevation
On the Earth, we are at the bottom of a huge ocean of air called the atmosphere.
The atmosphere pushes down on you like water in an ocean would.
At sea level, the atmosphere exerts a pressure of 100,000 pascals.

10. Question #2
As we go higher in the atmosphere what happens to the air pressure?
Why?

11. Fluids exert an upward force on objects.
The reason things can float in fluids (gases or liquids) is because the particles in the fluid push against the force of gravity on the object.
Buoyant Force- the upward force a fluid exerts on any object in the fluid.
The buoyant force exists because of the pressure differences in fluids.
The pressure in a fluid depends on depth only.

12. Pressure is determined by depth.
The top of the object has less pressure pushing on it than the bottom of the object.
The bottom of the object has more force pushing up than the top has pushing down.
Net Force = Upwards Force (Buoyant Force)

13. Buoyancy in Gases Buoyancy works in gases too! (Gases are FLUIDS!!!)
Air does not produce a big buoyant force so we tend to not feel it, but balloons use the buoyant force of air.

14. The size of the buoyant force equals the weight of the displaced fluid.
Archimedes’ Principle
More than 2000 years ago, a Greek guy named Archimedes studied water and its forces on objects.
He discovered that the buoyant force equals the weight of the displaced water.

15. Remember, density = mass/volume.
Floating and Sinking
How to figure out if something will float or sink:
Compare the upwards buoyant force with the force of gravity pulling down.
If both forces are equal, the object will not rise or sink.
If the buoyant force is greater, the object will float to the surface.
If the buoyant force is smaller, the object will sink.
Remember, density = mass/volume.

16. Question #3
What can you tell about the densities of Rubbing Alcohol compared to Dawn Dish Soap?
How do you know?