Physics Paper 2

What do scalar quantities have?

Magnitude only

What do vector quantities have?

Magnitude and direction

Examples of scalar quantities

• Mass

• Temperature

• Speed

• Energy

• Distance

• Time

• acronym: DT METS

Examples of vector quantities

• Displacement

• Weight

• Force

• Velocity

• Acceleration

• Momentum

• Gravity

• FW MAG DV

What is displacement?

Distance in a specific direction.

How can a vector quantity be shown?

• On an arrow.

• The length of the arrow represents the magnitude.

• The direction of the arrow represents the direction.

What is a force?

A push or a pull that acts on an object due to the interaction with another object.

Force is a vector quantity.

Measured in Newtons (N)

What is a contact force?

• A force in that acts between two objects that are physically touching.

• Examples of contact forces:

  • Friction force

  • Tension force

  • Air Resistance force

  • Normal Contact force

Friction

Two objects sliding past each other experience friction forces.

E.g. a box sliding down a slope.

Tension

An object that is being stretched experiences a tension force. For example in tug of war, there’s the force of tension pulling on the soldier.

Air resistance

An object moving through the air experiences air resistance. For example a skydiver falling through the air.

Normal contact force

An object on a surface experiences normal contact force. Normal contact force when the object is exerting a downward force on the table and at the same time the table exerts an upward force on the lamp. e.g. a book on a table.

Normal contact force can only happen if the two objects are in direct contact.

What is a non-contact force?

• A force that act between two objects that are not physically touching each other.

• Examples:

  • Magnetic force

  • Electrostatic force

  • Gravitational force

Magnetic force

• A force experience by any magnetic material in a magnetic field.

• Opposite magnetic poles (N-S OR S-N) attract each other.

• Like magnetic poles (N-N or S-S) repel each other.

Electrostatic force

• The force between two charged objects in an electric field.

• Opposite charges attract (+ and -)

• Like charges repel (- and -) or (+ and +)

Gravitational force

A force of attraction between all objects e.g. the gravitational force attracts the International Space Station to the Earth and the Earth to the International Space Station.

What does the mass of an object tell us?

• How much matter is in the object

• Measured in kg

• Mass is a scalar quantity

• The mass of an object does not depend on where the object is- mass remains the same in all locations.

What is weight?

• The force acting on an object due to gravity.

• Measured in Newtons

• Weight does depend on where it is as gravity isn’t the same everywhere.

What is gravitational field strength?

• A measure of the force of gravity in a particular direction.

• The gravitational field strength on Earth is 9.8 N/kg.

Weight formula

Weight= mass x gravitational field strength

N kg N/kg

What is the weight of an object directly proportional to?

The mass of the object

What can be used to measure weight?

A calibrated spring-balance- aka a newton metre.

Where is the weight of an object (force due to gravity) considered to act?

At a single point.

This is referred to as the centre of mass.

What is a resultant force?

A single force that has the same effect as all the original forces that act in a straight line.

What is thrust in airplanes?

Forward force provided by engine

What can a single force be resolved into?

Two components acting at right angles to each other. The two component forces together have the same effect as the single force.

What is work done?

• The energy transferred by a force when it moves an object through a distance.

• The distance must be in the line of action of the force.

Work done formula

Work Done (J) = Force (N) x Distance (m)

W=Fs

• Scientists also use the unit newton-metre

• 1 newton-metre = 1 joule

What happens to elastic materials when the forces acting on them are removed?

They always return to their original length.

What is elastic deformation?

When a material returns to it’s original length or shape after the forces that were

What needs to be done in order to change an object’s length or shape? (stationary objects only)

• More than one force needs to be applied.

• If only one force is applied to a stationary object, then the forces are no longer balanced.

• Therefore, the object would simply move rather than changing length or shape.

What happens to inelastic materials when the forces acting on it are removed?

They do not return to their original length or shape.

What’s inelastic deformation?

When a material doesn’t return to it’s original length or shape after the forces that were acting on it are removed.

Formula for force needed to stretch an elastic object.

Force= spring constant x extension

N

What is being used to stretch or compress an elastic object?

• Force

• Because elastic potential energy is stored in the object, the work done= the elastic potential energy.

• This is only true if the object is not inelastically deformed.

How to investigate the relationship between force and extension for a spring?

RP6

• Get a clamp stand, two bosses and two clamps

• Then place a heavy weight on the clamp stand to stop it falling over.

• Next attach a metre ruler and a spring to the clamps.

• Make sure the top of the spring is at 0 point on the ruler

• It’s crucial that the metre ruler is vertical otherwise the reading will be inaccurate.

• The bottom of the spring has a wooden splint attached as a pointer and this must be horizontal or the readings will be inaccurate.

• Now read the position of the pointer on the metre ruler-this is the y stretched length of the spring. (Length with no force attached)

• Next hang a 1 N weight on the spring and read the new position of the pointer on the metre ruler.

• Continue adding 1 N weights to the spring and reading the position of the pointer.

• Then calculated the extension produced by each weight by taking away the stretched length from the original unstretched length

• Then plot the extension against the weight.

• If asked the work out the the weight of a mystery object, measure the extension of the spring when the object is hanging from it and find the extension on the graph and use it to determine the weight.

What is the relationship between weight and extension?

• Linear

• If it goes through origin then it’s directly proportional.

What would be the result of the same experiment with a rubber band?

• Non-linear relationship between force and extension

How do we know the spring is elastic?

Because when the weight is removed the extension returns to 0.

What happens to the spring of too much force is added to it?

• It becomes inelastically deformed meaning that when the forces are removed the spring would still show an extension

• This makes the graph non-linear as the limit of proportionality has been exceeded.

How can the spring constant be determined from the graph?

• Use the linear part of the graph to get your force and extension values.

• Then use formula F=ke and rearrange to k=F/e to calculate constant.

• This value will be the same throughout as long the limit of proportionality hasn’t been exceeded

What is the moment of a force?

The turning effect of the force

What is the formula for calculating moments?

Moment (Nm)= Force (N) x Distance (m)

What is needed in order to calculate a moment?

For the distance to be perpendicular from the line of action of the force to the pivot.

Describe a balanced moment

• A sea saw that’s balanced about the centre.

• Each person is applying a moment due to their weight.

• The person on the right is applying a moment in the clockwise direction and the person on the left is applying a moment in the anti-clockwise direction.

• These are called clockwise and anti-clockwise moments

• Because the sea saw is balanced the clockwise moment must equal the anti-clockwise moment.

• In other words the force x distance in the clockwise direction= the force x distance in the anti-clockwise direction.

• This can be used to calculate either the force or the distance from the pivot.

Why do objects topple?

Because the line of action of the force/weight lies outside the base of the object.

What do levers do?

• Transmit the turning effect of the force from one side of the pivot to another. The aim is to get a large output force out of a relatively small input force. (Force multipliers)

• If the input and output forces are on different sides of the pivot then they’ll act in different directions whereas if the input and output forces are on the same side of the pivot then they’ll act in the same direction.

• The output force is generally closer to the pivot then the input force.

What do gears do?

Transmit turning effects.

• Gear B has double the radius of Gear A so the turning effect of it is double the turning effect of gear A.

• But because Gear A rotates twice as Gear B rotates once the work done from both gears are equal.

When particles in fluids collide with the walls of the container, they exert a force, where does this force act?

At right angles to the wall (along the normal)

Formula for pressure exerted by fluids

Pressure (Pa) = Force normal to the surface (N)/ area of that surface (m²)

What is the atmosphere?

A thin layer of air around the Earth.

Where is the atmosphere most dense?

• At the surface of the Earth

• This means there are the greatest number of air molecules in a given volume at the Earth’s surface.

What happens to the atmosphere as we increase in altitude?

• It gets less dense meaning the number of gas molecules in a given volume decreases.

What is the pressure of the atmosphere caused by?

• Air molecules colliding with a surface

Why does atmospheric pressure decrease as altitude increases?

• Because the atmosphere is less dense, meaning the number of air molecules in a given volume decreases.

• The pressure of the atmosphere is caused by air molecules colliding with a surface so because there are less air molecules in a given volume, the number of collision between the air molecule and a surface decreases meaning atmospheric pressure decreases with height.

Why does a packet is crisps inflate on an aeroplane?

• At ground level, the air pressure inside the bag is the same as the air pressure outside the bag.

• However, when aeroplanes are flying, the air pressure in the cabin is kept at a slightly lower level than the air pressure on the ground.

• This means the air pressure outside the bag is lower than the air pressure inside the bag causing it to inflate.

What would happen if we made holes in the side of the container?

• The water squirts out of the container.

• The water from the bottom hole squirts out much further than the water from the top hole.

• That is because the water at the bottom of the container is at a higher pressure than the water at the top as there’s more water above it therefore more weight pushing it down.

Formula for pressure of a column of liquid

Pressure (Pa) = height of the column (m) x density of liquid (kg/m³) x gravitational field strength.

Why does the pressure of a liquid increase with depth?

• Because as the depth increases there is a greater weight of liquid acting downwards.

Why does the pressure of a liquid increase with the density?

Because liquids with a greater density have a greater weight acting downwards.

Why does the level of liquid rise when an object is placed in it?

Because the objects has displaced it.

• The size of the upthrust acting on the object is the same as the weight of water displaced by the object.

• This means if the upthrust can displace its own weight of water then the upthrust will be equal to the objects weight, meaning it will float.

Why does the level of liquid rise when an object is placed in it?

Because the objects has displaced it.

• The size of the upthrust acting on the object is the same as the weight of water displaced by the object.

• This means if the upthrust can displace its own weight of water then the upthrust will be equal to the objects weight, meaning it will float.

What happens when an object that’s less dense than water is being placed in water?

• Because it’s less dense, it only has to displace a small volume (less than its own volume) of water before the weight of water displaced equals the weight of the object.

• Then the upthrust will equal the weight of the object and the object will float and it will float high in the water.

• However if an object has the same density as water, the object has to displace its own volume of water in order for the weight of water displaced to equal the weight of the object.

• Then the upthrust will equal the weight of the object and the object will float, the surface of the object being at the surface of the water.

• If the object is more dense than water then it cannot displace a volume of water to equal its own weight, therefore the weight of the object will be greater than the upthrust so the object sinks.

What does distance tell us?

• How far an object moves.

• Doesn’t involve direction

• This means it’s a scalar quantity

What does displacement tell us?

• The distance an object moves in a straight line from the start point to the finish point.

• Also tells us the direction of that straight line

• It’s a vector quantity

Formula for speed

Speed (m/s) = distance (m)/ time (s)

v=s/t

• Speed tells us the rate at which a distance is travelled per second.

Normal walking speed

1.5 m/s

Running speed

3 m/s

Cycling speed

6 m/s

Car on main road speed

13 m/s

Fast train in UK speed

50 m/s

Cruising aeroplane speed

250 m/s

Speed of sound in air

330 m/s

• This can vary e.g. sound travels faster on warmer days than colder ones.

What is velocity?

• Speed in a given direction.

• Vector quantity.

• Velocity is calculated with the speed formula, you just add direction

Velocity of an object moving at a constant speed in a circle.

• Although speed is constant, it’s constantly changing directions and because velocity is a vector quantit

What does the gradient on a distance-time

What does an upwards sloping curve on a distance-time graph represent?

• Acceleration as the object’s speed is constantly.

• To calculate speed at any point use gradient.

What does a downward sloping curve represent on a distance-time graph?

• Deceleration as the speed in constantly decreasing.

• To calculate speed at any point use gradient.

What does acceleration tell us?

• The change in an object’s velocity over a given time.

Formula for velocity

v=d/t

What does a horizontal line on a velocity-time graph tell us?

• The object is travelling at a constant velocity.

What does a straight line show on a distance-time graph?

• Object is moving at a constant speed.

What does an upward sloping line show on a velocity time graph?

Constant acceleration

What does a downward sloping line show on a velocity-time graph?

Constant deceleration

What does the total area under a velocity-time graph tell us?

• The distance/displacement travelled

• When we see constant acceleration or deceleration, we simply divide the graph into shapes and calculate their total areas.

• When the acceleration and deceleration are not constant, we count the squares and then estimate the total of the parts of squares.

• Or you could split each row and calculate area or triangle or trapezium and add up total area.

Formula for constant acceleration

v² - u²= 2as

final velocity² - initial velocity (m

When any object falls towards the surface of the Earth, what does it initially accelerate by?

• 9.8 m/s²

Describe skydiver who just jumped out of an aeroplane.

• He initially accelerates due to the force of gravity acting on the object.

• As the skydiver falls, he experiences an upward force of friction with the air particles- air resistance.

• After some time the force of air resistance balances the force of gravity.

• At this point the object stops accelerating and moves at a constant velocity.

• This is called the terminal velocity.

• This applies to any object falling through a fluid in this case the air.

What does the terminal velocity an object reaches depend on?

• The object, some objects experience a greater force of friction due to their shape so they will have a lower terminal velocity.

What’s Newton’s first law of motion?

• If the resultant force acting on a stationary object is 0, then the object will remain stationary.

• If the resultant force acting on a moving object is 0, the the object will continue moving with the the same speed in the same direction (with the same) velocity.

• Velocity will only change (object will accelerate) if there’s a resultant force acting on an object.

What force opposes and balances the driving force of a vehicle travelling at a constant velocity.

• Resistive forces

• The resistive forces include friction with the air and friction with the road.

What is Newton’s second law of motion?

• The acceleration of an object is directly proportional to the force acting on the object and inversely proportional to the mass of the object.

• This can be used to calculate the force needed to accelerate an object.

What is the formula for the force needed to accelerate an object?

Force (N) = Mass (kg) x Acceleration (m/s²)

Cars main road speed (UK)

13 m/s

Cars motorway speed (UK)

30 m/s

Acceleration from main road to motorway

• 2 m/s²

• For a typical family car that would require a force of 2000 N.

Inertia

• An object will stay stationary, or continue moving at the same speed and direction (with the same velocity) unless a resultant force is applied.

• This property of objects is called inertia.

What’s inertial mass?

• A measure of how difficult it is to change the velocity of an object.

• The inertial mass is defined as the ratio of the force needed to accelerate an object/ acceleration produced.

• An object with a large inertial mass will require a larger force to produce a given acceleration than an object with a smaller inertial mass.

What’s Newton’s third law of motion?

Whenever two objects interact, the forces they exert on each other are opposite and equal.