Chapter 2 Forces in Fluids

What is a fluid? A substance of variable shape; it takes on the shape of its container. A solid can be immersed in the fluid.

What is a fluid? The answer Takes on the shape of a container A solid can be immersed in a fluid

𝑃= 𝐹 𝐴 where F = mg Pressure A force that is being applied on the surface 2 Factors that affect Pressure are Force and Surface area The force being applied is often the force of Gravity (weight) 𝑃= 𝐹 𝐴 where F = mg

How does a snowshoe work? Remember this? 𝑃= 𝐹 𝐴

Pressure and a Liquid Depends on: The depth, How deep an object is The density of a liquid

Depth How far below the surface an object is The more water above you, the greater the pressure. http://www.calctool.org/CALC/other/games /depth_press

Density Density is a relationship between the mass of a substance and how much space it occupies. 𝐷= 𝑚 𝑣 The smaller the density, the lower the pressure. The higher the density, the greater the pressure.

Factors Influencing pressure in a liquid Factor variation Result Depth Increase in depth Higher pressure Decrease depth Lower pressure Density Higher density Lower density

You are 200m below the ocean surface Which of the following applies? There would be a lower pressure than at the surface There would be a greater pressure than at the surface.

Between maple syrup(density 1. 37g/mL) and water(1 Between maple syrup(density 1.37g/mL) and water(1.00g/mL), which one will have the greatest pressure? Water Maple Syrop

Pressure in a Gas Pressure depends on the number of collisions between the particles Depends on 3 factors Temperature Volume And the number of particles

Pressure and temperature The higher the temperature the faster the molecules move the higher the number of collisions. the greater the pressure

Pressure and volume The greater the volume The more room the molecules have to move around. The fewer the collisions The lower the pressure

Number of particles and pressure. The higher the concentration the closer the particles are to one an other. The more likely they are to the collide The higher the pressure

Factors influencing Pressure in a Gas Factor Variation Result Temperature Higher temperature More pressure Lower temperature Less pressure Volume Higher gas volume Lower pressure Lower gas pressure Higher pressure Number of gas particles Higher number Lower number

Pascal’s Principle When pressure is applied to one point of a fluid the rise in pressure is transmitted throughout the fluid. States that an increase in the pressure of an enclosed fluid is transmitted uniquely and uniformly in all direction -

Blaise Pascal (1623-1662) A French mathematician, physicist and religious philosopher The shape of a container has no effect on pressure. Pressure applied to an enclosed fluid is transmitted to every part of the fluid as well as the wall of a container.

Remember fluids A fluid can take on the shape of any container, consists of both a gas and a liquid What is the main difference between a gas and a liquid?

Pascal’s principle and Hydraulics Any change in pressure applied at any given point is transmitted undiminished throughout the fluid. Pressure has to be the same everywhere Since liquids are incompressible, the volume will remain unchanged

Force can be transmitted over a Distance In order to keep the pressure the same, the volume needs to remain constant.

Car brakes work off of Pascal When we step on the brakes, the pressure is transmitted through the break fluid and evenly to the pads

Why do your brakes get soft when there is air in the system Why do your brakes get soft when there is air in the system? How can you fix it?

What happens if the area of the two piston’s are not the same? Since Pressure must be the same and P =F/A Pascal’s principle 𝐹1 𝐴1 = 𝐹2 𝐴2

Answer Volume = Area x h if the area increases, then the height must decrease

When the small piston is pressed, the pressure is distributed evenly When the small piston is pressed, the pressure is distributed evenly. Since the volume remains the same and the area increase, the distance must decrease

Hydraulics Press

Why do airplanes or birds fly?

The Answer, Bernoulli’s principle (1738) When the speed of a fluid increases, it pressure decreases. The Principle was observed by Bernoulli, while watching water flow through the pipes.

Bernoulli’s Discovery

Ping Ball demo

If you were to hold two pieces of paper next to each other and blow in between, what would happen? Once you have your prediction, Try it What happened?

Bernoulli’s and a plane

Lift in a plane Particles above the wing move faster than below. Faster particles =lower pressure The wing goes to where the pressure is less.

Four forces of flight

lhttp://www.aviation-for-kids.com/Lift.html Bernoulli's clip

What happens to an object when you drop in water?

What determines what happens to the object?

Archimedes (287-212 BC)

Archimedes discoveries Volume of an object can be determined by the volume of water displaced. Pressure of water increases with depth. The buoyant force = the weight of the fluid displaced.

Pressure in a fluid Pressure depends on depth, the deeper you are the more pressure Since the pressure is less at the top of the object vs the bottom, there is an upward force acting on the object (buoyancy)

Is buoyance the only force?

Forces acting on an immersed object

Archimedes' Principle An object immersed in a fluid is subjected to a buoyant force equal to the weight of the fluid displaced

Buoyant force: Is the same as the weight of the water displaced by the object Apparent Force: How much the object weights in the Fluid.

Float or sink? Float: When the buoyant force is greater than the force of gravity acting on the object Maintain depth(Suspension): When the buoyant force = the force of gravity. Sink: when the buoyant force is less than gravity

Hot air balloons The buoyant force is equal to the weight of the air outside the balloon that is displaced The buoyant force must be great than the weight of the hot air and balloon.

How does a Boat stay afloat?

What about a submarine?

Why do you float in the Dead sea?

Density and buoyancy The greater the density of the liquid, the less liquid is displaced, the object goes higher up

Project time Get into groups of 3 or 4. Determine which principle you are using, find a common day or technological example that applies to the principle. Explain and share it with the class