Chapter 3

Question 1

Moment =

Answer 1

moment = force x distance

Question 2

principle of moments

Answer 2

If an object is in equilibrium, the sum of the clockwise moments about any point is equal to the sum of the anticlockwise moments about that point
(clockwise moment = anticlockwise moment)

Question 3

Conditions for equilibrium (balance)

Answer 3

The sum of the forces in one direction must equal the sum of the forces in the other direction
The principle of moments

Question 4

Finding the centre of mass

Answer 4

When a plane object is hanging from a point, it will rotate so that its centre of mass is directly below the point

Question 5

States of equilibrium

Answer 5

Stable - centre of mass remains over base even when tilted
Unstable - the centre of mass remains over the base for only a miniscule amount of time as the base is so small
Neutral - the centre of mass is always over the base, regardless of position

Question 6

Elastic material

Answer 6

Any material that returns to its original shape when the force that changed its shape is removed.
Elastic materials have an elastic limit after which they stop being elastic.

Question 7

inelastic (plastic) material

Answer 7

Any material that stays in its new shape even after the force that caused the shape change has been removed

Question 8

Hooke’s Law

Answer 8

Beneath a material’s elastic limit, the extension is proportional to the load.

Question 9

Spring constant (k) =

Answer 9

spring constant = load/extension (f/x)

Question 10

Pressure =

Answer 10

pressure = force/area

Question 11

Unit of pressure

Answer 11

Pascals, Pa (1Pa = 1N/m^2)

Question 12

pressure in liquid =

Answer 12

pressure in liquid = density x g x height

Question 13

Characteristics of pressure in liquid

Answer 13

Pressure acts in all directions
pressure increases with depth
Pressure depends on the density of the liquid
Pressured doesn’t depend on the shape of the container
Pressure doesn’t depend on volume

Question 14

Boyle’s Law

Answer 14

For a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume OR P1V1=P2V2

Question 15

A gas that obeys Boyle’s Law is called…

Answer 15

an ideal gas

Question 16

Characteristics of an ideal gas

Answer 16

• Obeys Boyle’s Law
• Have low density
• Have a temperature well above their liquefying point
• Is not full of water vapour

Question 17

Explain Boyle’s Law

Answer 17

• A gas is made up of tiny moving particles
• That experience no attraction to one another
• They move about freely at high speed
• The higher the temperature, the faster they move
• The faster they move, the higher the pressure is

Question 18

How to find pressure of gas supply using a manometer

Answer 18

• Measure difference in height
• Calculate pressure of gas using pressure = height (difference) x g x density
• Add this value to atmospheric pressure

Question 19

How to find pressure using a barometer

Answer 19

Pressure = height x g x density

Question 20

Standard atmospheric pressure

Answer 20

100,000 Pa or 1 atm

Question 21

Centre of mass

Answer 21

The centre of mass of an object is the point through which the weight of that object acts in a uniform gravitational field