Transmitting Pressure in a Fluid

Transmitting Pressure in a Fluid

Think about this… Sirens of a fire truck pierce the morning

silence while black smoke rolls into the air. Soon the firefighters are on their ladders and have the blaze under control.

Thanks to equipment on the fire truck, this story has a happy ending.

Fire trucks use fluids to lift the ladder and its equipment to great heights.

You will soon learn how.

Think about this… Sirens of a fire truck pierce the morning

silence while black smoke rolls into the air. Soon the firefighters are on their ladders and have the blaze under control.

Thanks to equipment on the fire truck, this story has a happy ending.

Fire trucks use fluids to lift the ladder and its equipment to great heights.

You will soon learn how.

Take a look… Pg. 87 Figure 8

Take a look… Pg. 87 Figure 8

As we learned in the last section, a fluid exerts pressure on any surface it comes in contact with.

For example water in a bottle exerts pressure on the entire inside surface of the bottle- up, down, and sideways.

If you push the stopper down even farther, the water has nowhere to go, so it presses harder on the inside surface of the bottle. The pressure in the bottle increases everywhere in the bottle.

As we learned in the last section, a fluid exerts pressure on any surface it comes in contact with.

For example water in a bottle exerts pressure on the entire inside surface of the bottle- up, down, and sideways.

If you push the stopper down even farther, the water has nowhere to go, so it presses harder on the inside surface of the bottle. The pressure in the bottle increases everywhere in the bottle.

Pascal’s PrinciplePascal’s Principle

The fact that pressure increases by the same amount throughout an enclosed, or confined fluid was discovered in the 1600’s by Blaise Pascal.

When force is applied to a confined fluid, an increase in pressure is transmitted equally to all parts of the fluid. This relationship is known as Pascal’s Principle.

The fact that pressure increases by the same amount throughout an enclosed, or confined fluid was discovered in the 1600’s by Blaise Pascal.

When force is applied to a confined fluid, an increase in pressure is transmitted equally to all parts of the fluid. This relationship is known as Pascal’s Principle.

Force PumpsForce Pumps

What do you think would happen if you increased the pressure at one end of a fluid in a container with a hole at the other end?

Think about a squeeze bottle (Ketchup, mustard) or a medicine dropper.

Because it is not a confined or closed container, the fluid is pushed out of the opening.

This example shows how a force pump works. A force pump causes a fluid to move from one place to another by increasing the pressure in the fluid.

What do you think would happen if you increased the pressure at one end of a fluid in a container with a hole at the other end?

Think about a squeeze bottle (Ketchup, mustard) or a medicine dropper.

Because it is not a confined or closed container, the fluid is pushed out of the opening.

This example shows how a force pump works. A force pump causes a fluid to move from one place to another by increasing the pressure in the fluid.

Your HeartYour Heart

Another example is your heart. Your heart contains two force pumps. One of them pumps blood to the lungs, where it can pick up oxygen from the air you breathe. This blood now carrying oxygen returns to the heart. It is then pumped to the rest of the body by the second pump.

Another example is your heart. Your heart contains two force pumps. One of them pumps blood to the lungs, where it can pick up oxygen from the air you breathe. This blood now carrying oxygen returns to the heart. It is then pumped to the rest of the body by the second pump.

Using Pascal’s PrincipleUsing Pascal’s Principle Look on page 88 at Figure 9 and let’s read how a

hydraulic device works. In Figure 9A we see that the force exerted on the left

piston is transmitted to the right piston. In Figure 9B we see the same however the surface area

of the right piston as increased from one square meter to 20 square meters.

Since the surface area is 20 x larger we multiply the pressure on the left side of the piston 20 x allowing us to lift a car with very little force.

If the force on the left side of the piston is 500 newtons, what is the total increase of pressure on the right side?

___________________ newtons

Look on page 88 at Figure 9 and let’s read how a hydraulic device works.

In Figure 9A we see that the force exerted on the left piston is transmitted to the right piston.

In Figure 9B we see the same however the surface area of the right piston as increased from one square meter to 20 square meters.

Since the surface area is 20 x larger we multiply the pressure on the left side of the piston 20 x allowing us to lift a car with very little force.

If the force on the left side of the piston is 500 newtons, what is the total increase of pressure on the right side?

___________________ newtons

Hydraulic SystemsHydraulic Systems

Hydraulic systems are designed to take advantage of Pascal’s principle.

A hydraulic system multiplies a force by applying the force to a small surface area. The increase in pressure is then transmitted to another part of a confined fluid, which pushes on a larger surface area.

This is how the firefighters are able to lift the ladder on the fire truck and how a car is able to stop using the brake system.

Hydraulic systems are designed to take advantage of Pascal’s principle.

A hydraulic system multiplies a force by applying the force to a small surface area. The increase in pressure is then transmitted to another part of a confined fluid, which pushes on a larger surface area.

This is how the firefighters are able to lift the ladder on the fire truck and how a car is able to stop using the brake system.

Brake SystemBrake System

In figure 10 on page 88 we can see how a hydraulic brake system works.

When the driver pushes down on the brake pedal, he or she pushes a piston. The piston exerts pressure on the brake fluid.

The increased pressure is transmitted through the brake lines to pistons within the wheels of the car. Each of the pistons pushed on a brake pad. The brake pad then rubs against the brake disc, and wheel’s motion is slowed down by the force of friction.

Because the brake system multiplies force, a person can stop a very large car with only light push on the brake pedal.

In figure 10 on page 88 we can see how a hydraulic brake system works.

When the driver pushes down on the brake pedal, he or she pushes a piston. The piston exerts pressure on the brake fluid.

The increased pressure is transmitted through the brake lines to pistons within the wheels of the car. Each of the pistons pushed on a brake pad. The brake pad then rubs against the brake disc, and wheel’s motion is slowed down by the force of friction.

Because the brake system multiplies force, a person can stop a very large car with only light push on the brake pedal.

Pascal’s Principle in Nature

Pascal’s Principle in Nature

The sea star shown in figure 11 uses a natural hydraulic system called water vascular system in order to move.

Sea stars have rows of suckers at the ends of their hollow tube feet.

Each tube is filled with fluid. A valve is located at each foot. When the valve closes, the foot becomes a hydraulic container.

As the sea star contracts different muscles, it changes the pressure in the fluid.

The change in pressure causes the tube foot to either push down or pull up on the sucker.

By the coordinated action of all of its tube feet, a sea star is able to move - even to climb straight up rock surfaces!

The sea star shown in figure 11 uses a natural hydraulic system called water vascular system in order to move.

Sea stars have rows of suckers at the ends of their hollow tube feet.

Each tube is filled with fluid. A valve is located at each foot. When the valve closes, the foot becomes a hydraulic container.

As the sea star contracts different muscles, it changes the pressure in the fluid.

The change in pressure causes the tube foot to either push down or pull up on the sucker.

By the coordinated action of all of its tube feet, a sea star is able to move - even to climb straight up rock surfaces!