Forces, Density And Pressure

Question 1

Define density.

Answer 1

The ratio of mass to volume of a substance.
Density = mass / volume
Density tells us about how closely packed particles of a substance are.

Question 2

What are the volume formulas for a cube, sphere and a cylinder?

Answer 2

Cube: V = pi r3

Cylinder: V = pi r2 h OR V = pi d2 h / 4

Sphere: V = 4 pi r3 / 3 OR V = pi d3 / 6

Question 3

Define pressure

Answer 3

The normal force per unit area.
Pressure = Force / Area

At an angle: Pressure = F sin theta / Area

Pressure exerted onto the incline/slope:

P = 4 mg cos theta / pi d2

Question 4

Define fluid.

Answer 4

Any substance that can flow.

Question 5

What is the formula for pressure in fluids?

Answer 5

Pressure = density x gravity x depth

Question 6

Describe the manometer.

Answer 6

• is a U shaped tube
• used to measure pressure difference
• at ATM, the liquid inside the tube will be at the same height
• if a gas supply is added to one side, we can measure the pressure due to the gas by taking the change in height from the left and right sides of the tube
• therefore, change in pressure = density x gravity x change in height
• however, the total gas pressure is ATM + change in pressure.

Question 7

Describe Archimedes Principle.

Answer 7

The principle states that an immersed object displaces its own weight.
V = volume of displaced liquid
p* = density of displaced liquid
U (Upthrust) = W (Weight)
U = mg
p* = m/V therefore m = p* V
Therefore U = p* V g

U = p* V g = W

Question 8

What causes upthrust?

Answer 8

Caused by the difference in pressure at the bottom and top of the immersed object.
P bottom > P top