Chapter 3 Flashcards
Moment =
moment = force x distance
principle of moments
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)
Conditions for equilibrium (balance)
The sum of the forces in one direction must equal the sum of the forces in the other direction
The principle of moments
Finding the centre of mass
When a plane object is hanging from a point, it will rotate so that its centre of mass is directly below the point
States of equilibrium
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
Elastic material
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.
inelastic (plastic) material
Any material that stays in its new shape even after the force that caused the shape change has been removed
Hooke’s Law
Beneath a material’s elastic limit, the extension is proportional to the load.
Spring constant (k) =
spring constant = load/extension (f/x)
Pressure =
pressure = force/area
Unit of pressure
Pascals, Pa (1Pa = 1N/m^2)
pressure in liquid =
pressure in liquid = density x g x height
Characteristics of pressure in liquid
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
Boyle’s Law
For a fixed mass of gas at constant temperature, the pressure is inversely proportional to the volume OR P1V1=P2V2
A gas that obeys Boyle’s Law is called…
an ideal gas
Characteristics of an ideal gas
- Obeys Boyle’s Law
- Have low density
- Have a temperature well above their liquefying point
- Is not full of water vapour
Explain Boyle’s Law
- 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
How to find pressure of gas supply using a manometer
- Measure difference in height
- Calculate pressure of gas using pressure = height (difference) x g x density
- Add this value to atmospheric pressure
How to find pressure using a barometer
Pressure = height x g x density
Standard atmospheric pressure
100,000 Pa or 1 atm
Centre of mass
The centre of mass of an object is the point through which the weight of that object acts in a uniform gravitational field
