Y9 - Physics Revision

Question 1

What is Speed

Answer 1

Speed is a measure of how far something travels in a particular time. It is measured in Meters per Second.

Question 2

Speed Equation:

Answer 2

Speed (m/s) = Distance Travelled/Time Taken (s)

Question 3

What is Instantaneous Speed?

Answer 3

Instantaneous Speed is the speed that an object is travelling in that single moment in time.

Question 4

What is Average Speed?

Answer 4

Average Speed is the speed of an objects after travelling over a certain distance and time. You can work out average by using:

Average Speed=Total Distance/Total Time

Question 5

What is Relative Motion?

Answer 5

Relative Motion means how fast one object is travelling compared to another object to another. This means that the speed between the two objects are relative.

If 2 cars are moving towards each other at 30mph, then their relative speed is 60. If they are moving in the same direction, at the same speed, their relative speed is 0.

Question 6

What is a Distance-Time Graph?

Answer 6

A Distance-Time Graph is a useful way of showing how something moves over a certain period of time.

Question 7

What is happening in a Distance-Time Graph when the line is horizontal.

Answer 7

The person is not moving.

Question 8

What is happening when there is a curve in the Distance-Time Graphs

Answer 8

When there is a curve in the Graph, the object is accelerating (if the line is curving up) or slowing down (if the line is curving down). This shows you show quickly the object is changing speed.

Question 9

How does gas pressure build

Answer 9

Gas pressure builds when the air particles collide with it’s container’s walls, which builds up gas pressure. (The container has to be closed).

Lots of collisions make a high pressure, fewer collisions make a low pressure.

Question 10

What happens when you decrease the volume of the gas’s container?

Answer 10

If you make the container smaller with the same amount of gas, then the pressure will increase, as there will be more collisions.

Question 11

What happens when you increase the volume of the gas’s container?

Answer 11

If you make the container bigger with the same amount of gas, then the pressure will decrease, as there will be less collisions.

Question 12

What happens when you decrease the temperature of the gas’s container?

Answer 12

If you make the temperature colder with the same amount of gas, then the pressure will decrease, as there will be less kinetic from the lack of heat which will leave the particles with less energy, meaning they move slower and collide less.

Question 13

What happens when you increase the temperature of the gas’s container?

Answer 13

If you make the temperature hotter with the same amount of gas, then the pressure will increase, as the kinetic energy from the heat will energise the particles, meaning they move faster and collide more.

Question 14

What happens when you increase the amount of gas in it’s container
(Compress the Gas)

Answer 14

When you increase the amount if gas in it’s container (compress it), then there will be less collisions, because the gas can’t move around as quickly or freely as it would like, meaning there are less collisions and therefore, less pressure.

Question 15

What happens when you decrease the amount of gas in it’s container?
(Decompress the Gas)

Answer 15

When you decrease the amount if gas in it’s container (decompress it), then there could be more collisions, because the gas can move around as quickly or freely likes. However, this does not always result in more pressure, because if there is way to few particles then, they’ll only be able to collide very few times, meaning that there is not always more pressure anyway, but if there are enough then it could increase too.

Question 16

What is Atmospheric Pressure?

Answer 16

Atmospheric Pressure is the pressure that a gas exerts on a certain object (this pressure goes inwards). For example, the air exert an Atmospheric Pressure on Humans. You don’t feel this pressure because it is cancelled out by the pressure of liquids and solids, in your body, which pushes outwards.

Question 17

Why is Atmospheric Pressure higher, when closer to sea level?

Answer 17

This is like this because gravity pull the air particles towards the Earth’s core, so there will naturally be more particles near the bottom of the atmosphere, rather than at the top, meaning the bottom is denser and the top is less dense. This is why the air is thin on mountains and gas has a high density at sea level

Question 18

What is Liquid Pressure?

Answer 18

Liquid pressure only happens in liquids and the liquid molecules are pushing down on each other and on surfaces (including humans). This pressure acts in all directions.

Question 19

Is Liquid Compressible or not and why?

Answer 19

Liquid is incompressible, because pretty much all of the particles in a liquid are touching each other and, therefore, can’t be compressed.

Question 20

Why does the wall of a dam always slant outwards?

Answer 20

This is because the deeper the water gets, the more pressure there is on surfaces touching it. It’s because the weight of the water above it. This means that if a lake is quite shallow, there is little pressure at the bottom, but if there was another lake that was a lot deeper, it would have more pressure at the bottom.

Question 21

Why do things float?

Answer 21

Liquid Pressure pushes in all directions, which means in also pushes upwards to create upthrust, which can keep things afloat. Upthrust acts on any floating or submerged object. An object will float is there are more water molecules hitting the bottom of it, than air molecules hitting the top of it. If the area of an object is too small,there won’t be enough upthrust to make it float.

Question 22

What is the Pressure exerted by Solids?

Answer 22

For example, humans exert pressure on the ground. The pressure that solids exert is how much force (Newtons) is applied over a certain area. The pressure acts in a direction that is 90° or normal to the surface. When things are spread out over a large area, the pressure will be less, when it is spread out over a smaller area, the pressure will be greater.

Question 23

What is Pressure Measured in?

Answer 23

Can be calculated in Newtons per Meter Squared (N/m^2), or N/cm^2, or even N/mm^2

And Is:

Measured in Pascals (pa)

Question 24

Pressure Equation

Answer 24

Pressure (N/m^2) = Force (N)/Area (m^2)

Question 25

What is a turning force?

Answer 25

A turning force is the force that acts over a certain distance from a pivot. The turning effect of a force is called a moment. The moment depends on the force being applied and how far away it is from the pivot. All the weight of an object on another seems to act through the centre of gravity/mass. If the centre is above the point, there is no turning force. If it is to the left or right, there is a turning force.

Question 26

Moment Equation

Answer 26

Moment (mn) = Force (N) x Perpendicular Distance from Pivot (m)

Question 27

What happens with moments of the left and right hand side?

Answer 27

It’s simple really, the moment of the weight on the left hand side will go anti-clockwise and the moment of the weight on the right will go clockwise. When the moments are balanced, the object holding the weight will stay at a 90° angle in equilibrium.

Question 28

What happens when the sum of the moments are equal.

Answer 28

When both moments are equal, then the object reaches equilibrium. This is the law of moments.