Chapter 3: Forces and Pressure

Graph

b- shows what happens when the load is removed.

Graph a

is an extension-load graph for a spring

Graph b

graph shows what happens when the load is removed

Define Moment.

It is the turning effect of a force.

Give equation for moments.

Moments= Force x Perpendicular Distance

What is the principle of moments (equilibrium)?

It states that the sum of the clockwise moments about any point is equal to the sum of the anticlockwise moments about that same point.

What is centre of mass (gravity)?

It is the effect of gravitational forces act on an object as a single resultant force (the object's weight).

Define stable equilibrium.

It is when the centre of mass rests over a large base (making tripping difficult).

Define unstable equilibrium.

It is when the centre of mass rests over a very small base (making tipping easy).

Define neutral equilibrium.

It is when the centre of mass rests over a round base, allowing movement when force is applied (allowing rolling).

What are the conditions of equilibrium.

1) the sum of the forces in one direction must equal the sum of the forces int he opposite direction.
2) the principle of moments must apply.

Define pressure.

It is the concentration of a force.

What is the SI unit of pressure?

Pascal (Pa)

State equation for pressure.

Force / Area

State equations for pressure in liquids.

P = density (ρ) x gravity (g) x depth in liquid (h)

Properties of pressure in liquids

1) pressure acts in all directions
2) pressure increases with depth
3) pressure depends on the density of the fluid
4) pressure does NOT depend on the shape of the container/vessel

What is the use of barometer?

It is the instrument used to measure atmospheric pressure typically with Mercury (Hg).

What is the use of manometer?

It is instrument used to measure pressure differences compared to atmospheric pressure.

What is Hooke's Law?

It states that the extension of a spring is proportional to the load applied to it, provided the limit of proportionality is not exceeded.

What is limit of proportionality?

It is the full extension of an elastic object until further force extends more than the spring constant

State equation for hooke's law.

F = k * x

Define boyle's law.

It is for a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume.

State equation for boyle's law.

P1 x V1 = P2 x V2

Why is the pressure of the gas inversely proportional to volume in boyle's law?

As volume decreases, the gas volume comes close together. As a result they get a chance a to collide more frequently with the walls of container thereby exerting a greater pressure force per unit area, hence pressure increases.

Where is hydraulic system used?

Common use in pedal brakes of car.