Hydraulic Machines

WALT- Explain how water pressure may help usWILF – Notes taken, questions answered

1. What do we mean when we say that a machine is “hydraulic”?

• ________________________________________________________________

2. Fill in the gaps by crossing out the incorrect phrases:

• There are the four key properties of liquids that are important to remember when looking at hydraulic machines:

1) Liquids will always (flow to take the shape of their container/ keep the same shape) no matter what container you use.

2) If you have a fixed amount of liquid, then its volume (can change / will always stays the same) when pressure is applied to it.

3) The pressure in a fluid (acts in all directions / acts in the direction of the applied force).

4) If a constant force acts throughout a liquid, the pressure (can vary / stays the same) throughout the liquid.

Each of these properties can be explained by thinking of the way particles that

make up the fluid move and interact with each other. How?

3. A mechanic wants to inspect the bottom of a car for a leak. She tries to lift the car using a hydraulic lift.

a) On the diagram overleaf, draw and label arrows to show the direction in which each of the

following forces act:

• The mass of the car acting on its piston• The force exerted by the mechanic on her

piston• The hydraulic force of the liquid acting on the

car’s piston

• b) The area underneath the mechanic’s piston is 0.1m2, and the area underneath the car’s piston is 10m2. If the car weighs 1000kg, how much force does the mechanic need to apply to lift it? (Hint: remember force is measured in Newtons, not kilograms!)

• **Bonus question**

• c) If the mechanic pushes her piston down by 2 metres, by what distance is the car lifted?

Pressure & Moments

Revision Questions

Calculate the pressure exerted in the following situations.

1. A 200 N weight with a surface area of 2 m2.

2. A 800 N man wearing shoes with a surface area of 400 cm2.

3. A 10 N bag of flour with a surface area of 200 cm2.

4. A 20 000 N car, assuming each tyre has a contact area of 100 cm2.

100 N/m2

2 N/cm2

0.05 N/cm2

2000 N/cm2

1.A workman tightening a nut applies a force of 100 N to his spanner, 0.2 m from the nut. What is the moment of force?

2.How can he increase the moment of force?

3.A panda weighing 400 N sits 1 m from the pivot on a see-saw. What is the moment?

4.How far away would a panda cub weighing 200 N have to sit on the other side to balance him?

20 Nm or 2000 Ncm

Increase Distance from Pivot/Force

400 Nm

2 m

Oh no!

• YouTube - Man Falls Through Roof 4 times!• YouTube - Dumb Woman Falls Through Ice

Spread the force over a greater area

Camels

Snow shoes

Caterpillar tracks

House foundations

I had a dream

Sharp?

Drawing pins

Pressure

Pressure = Force Area

N/m2 or Pa

N

m2

Pressure

Pressure = Force Area

N/m2 or Pa

N

m2

F

AP x

Can you copy this please?

An example

A woman has a weight of 500N and one of her shoes has an area of 150 cm2. A man of weight 700 N has a shoe area of 360 cm2 (one shoe). What is the pressure beneath their feet?

An example

Mrs Rayner has a weight of 500N and one of her shoes has an area of 150 cm2. Mr Rayner has a weight of 700 N has a shoe area of 360 cm2 (one shoe). What is the pressure beneath their feet?

Mrs Rayner’s pressure = Force/area = 500/(2 x 150) = 1.67 N/cm2

Man’s pressure = Force/area = 700/(2 x 360) = 0.97 N/cm2

Calculating your own pressure

Remember your weight in Newtons is equal to your mass in kilograms multiplied by 10.

Calculating your own pressure

Remember your weight in Newtons is equal to your mass in kilograms multiplied by 10.

Can you do the calculations carefully and neatly on the graph paper to show your

pressure (don’t forget you have two feet!) and stick it in your book

Pressure under a car

Really nice car

Pressure under a car

• Mass = 2000kg• Weight = mg = 2000x10 = 20000N• Area = 2 x 100mm x 150 mm + 100mm 250

mm• Pressure = ?

Let’s try some questions!