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Fluids and Pressure

Middle school science lesson about fluids and pressure

Dee Corbie

on 30 November 2016

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Transcript of Fluids and Pressure

2. Change the mass
of the object
Fluids and Pressure
What are Fluids?
- any material that can flow and that take the shape of its container.
Fluids flow because their particles are
spread out
easily move past each other.
liquids and gases
What is pressure?
is the measure of how much force is acting on an area.
When you pump up a tire, air molecules are moving around constantly bumping into each other and against the walls of the tire, creating pressure.
What are two familiar fluids that exert pressure?
So the question is
how is pressure calculated
pressure = force divided by area
The unit for pressure is the
pascal (Pa)
Calculate the pressure of water pushing down on the bottom of a fish tank. The water pushes down with a force of 2,000 N and the area of the tank bottom is 0.4m2.
Atmospheric Pressure

Gravity pulls all objects with mass including air towards the center of Earth.
The atmosphere has weight and exerts pressure on objects below it including you and I.
Water Pressure

Gravity also pulls water towards the center of the Earth.
Underwater objects feel the pressure of the water above.
They also feel the weight of the atmosphere too!!
How does depth affect fluid pressure?
As an object travels deeper into the atmosphere, the more pressure it will feel because the greater weight of the air above it.
As an object travels deeper into water, the more pressure it will feel because of the weight above it.
P = 2,000 N divided by 0.4 m2
p= 2,000/.4
= 5,000 P
What are some examples of motion due to pressure?
Fluids move from areas of high pressure
to areas of low pressure.
What do you think is a buoyant force? Think about the root word in buoyant. How does that help you to determine the meaning?
buoyant force
is the upwards force that fluids exert on all matter.
Buoyant force is greater on the bottom of an object than on the sides or the top.
What can happen as a result of weight and buoyant force?
An object whose weight is equal to the buoyant force will float.
An object that has more weight than the buoyant force will sink.
An objects whose weight is less than buoyant force will rise until the weight and buoyant force are equal.
Do now: Describe Pressure and Depth and how they relate. Also, what do you think is bouyant force?
Why does an ice cube
float on water but not
on air?
An ice cube floats on
water because it is less
dense than water. But most
substances are more dense
than air.
Steel is almost 8 times
denser than water. So why
dont huge steel ships sink in
The secret of ships is density
Do now: Why dont huge steel
ships sink in water?
There are 3 ways
can change their

in which objects
is mass
per unit
1. the first way is
to change the
3. Lastly to change
overall density you
would change an object's
Cooler gas =
condensation outside
the glass
Liquid Nitrogen
A football player is tackled by another player and lands with the combined weight of both players on
his knee. If the combined weight of the players is 2400 N and the player’s knee measures 0. 8 m by
0.1 m, how much pressure is exerted on the turf when the player lands on his knee?
P= 2400n/ .8
P= 2400n divided by .8
Do now: One afternoon, you go
outside to find your younger
brother or sister standing
by her bike with a nail in her hand.
The bike has a flat tire. She wants to
know why the air came out of the
tire when she pulled the nail out. Explain why the air rushes out of a hole in a tire.
Turn and Talk- take the next 3 minutes
to discuss with your group : What is a fluid?
Question: does a gas qualify as a fluid?
Turn and talk- Use the next 3 mins to talk to your scholars and discuss what is pressure?
Anybody remembers what happens
with temperature and pressure
Air and water
The force of one
Pascal (1 Pa) is the
force of one newton exerted over an area of one square meter
(1 N/m2) Or
1Pa = 1 N/m2
Fluids exert pressure evenly in all directions
This is why bubbles get rounder
the longer you blow a bubble
When people say the
atmosphere around them
or talking about the Earth's
atmosphere what are they talking about?
What is the atmosphere?
The atmosphere is the layer of nitrogen, oxygen, and other gases that surrounds the Earth
Remember that water is a fluid, so it exerts pressure like the atmosphere does
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