Physics 4th Form BIG

What is a distance-time graph?

A graph that shows how the distance of an object moving in a straight line varies over time

What do distance time graphs show?

- Whether the object is moving at a constant speed

- How large or small the speed is

How does the gradient of a distance-time graph show speed?

- A straight line represents constant speed

- A straight line with a large gradient shows high speeds

- A straight line with a small gradient shows slow speeds

- A straight line with a gradient of 0 means that the object is stationary

How do distance-time graphs show changes of speed?

- Objects moving at a changing speed are represented by a curved line

- If the slope is increasing, the object is accelerating

- If the slope is decreasing, the object is decelerating

How would you find the gradient?

change in y / change in x = gradient

or

Rise/run = gradient

What is the speed of an object?

- The distance it travels every second

- Scalar quantity as it has magnitude but not direction

What is the equation for average speed?

Average speed = distance moved/ time taken

What is acceleration?

The rate of change in velocity

What is the equation for acceleration?

Acceleration = Change in velocity/ Time taken

What is a velocity-time graph?

A graph that shows how the velocity of a moving object varies with time

What does a velocity-time graph show?

- Whether the object is moving with a constant acceleration

- The magnitude of the acceleration

- Straight line represents constant acceleration

- The slope represents the magnitude of the acceleration

- A steep slope means large acceleration

- A gentle slope means small acceleration

- A positive gradient means acceleration

- A negative gradient means deceleration

- A flat line means acceleration is 0 + moving at a constant velocity

How can we find the displacement of a velocity-time graph?

- represents displacement

- Separate the areas into triangles and rectangles and fins the area

What is the equation for uniform acceleration?

(final speed)^2 = (initial speed)^2 + (2 x acceleration x distance moved)

What is a force?

A push or pull that arises from the interaction between objects

What is Gravitational force?

- There is a gravitational force of attraction between all objects with mass

- The more massive the object, the greater the greater the gravitational force exerted by it

- E.g. When a ball is thrown, the gravitational pull of the Earth pulls it towards the centre of the Earth

What is a Reaction force?

- When an abject rests on a surface, the surface exerts a push force on the object

- Force acts perpendicularly to the surface

- E.g. When a ball rests on the horizontal surface of the grass, the grass exerts a push force vertically upwards on the football

What is Friction?

- Frictional forces always oppose the motion of an object, causing it to slow down

- Friction occurs when 2 surfaces move over one another

- E.g. When a box is pushed across a carpet, the carpet exerts a frictional force on the box, slowing its motion

What is a Drag force?

- A type of frictional force that occurs when an object moves through a fluid

- The particles in the fluid collide with the object moving through it and slow its motion

- E.g. When a pebble is thrown into water, the water molecules flow against its solid surface, causing it to slow down

What is Air Resistance?

- A specific type of drag force and frictional force

- Occurs when particles of air collide with an object moving through it and slows its motion

- E.g. When a skydiver opens their parachute, air resistance opposes their motion and reduces their speed so it is safe to land

What is Thrust?

- A force produced by an engine that speed sup the motion of an object

- E.g. The engine of a car exerts a thrust force and increases its speed

What is Upthrust?

- When an object is fully or partially submerged in a fluid, the fluid exerts an upward-acting push force on the object

- E.g. A boat floats on a lake due to the upthrust exerted by the water in the boat

What is Electrostatic force?

- Occurs between two objects with charge

- Like charges repel and opposite charges attract

- E.g. When an electron gets close to a positively charged ion, the ion exerts a pull force on the electron (attraction)

- E.g. When an electron gets close to another electron, the electrons experience a push force from one another (repulsion)

What is Magnetic force?

- There is a magnetic force between objects with magnetic poles

- Like poles repel one another, opposite poles attract one another

- When a north pole gets close to a south pole, they experience a pull force from one another (attraction)

- When a north pole gets close to a north pole, they experience a push force from one another (repulsion)

What is Tension?

- Tension occurs in an object (rope or spring) that is stretched

- When a pull force is exerted on each end of an object, tension acts across the length of the object

What are the possible effects of forces?

Could change:

- Speed

- Direction

- Shape

What is a Scalar?

- A quantity that has magnitude but no direction

- E.g. mass or temperature

What is a Vector?

- A quantity that has both magnitude and direction

- E.g. weight or velocity

What is the difference between distance and displacement?

Distance is a scalar quantity whereas displacement is a vector quantity

What is the difference between speed and velocity?

Speed is a scalar quantity, Velocity is a vector quantity

What is a resultant force?

A single force that describes all of the forces operating on a body

- When multiple forces act on one object, the forces are combined to produce one net force

- Determines the direct in which the object will move and the magnitude of the net force experienced by the object

How can the resultant force be found?

- Forces working in opposite directions are subtracted from each other

- Forces working in the same direction are added together

- If the forces acting in opposite directions are equal in size, there will be no resultant force

What does it mean if the resultant force is 0?

The object is either stationary or travelling at a constant speed

What is the equation for Resultant force?

Resultant force (N) = Mass (kg) x Acceleration (m/s²)

What is weight?

The force experienced by an object with mass when placed in a gravitational field

What is the difference between weight and mass?

Mass is a scalar quantity whereas Weight is a vector quantity

What is the equation that links weight, gravitational field strength and mass?

Weight (N) = Mass (kg) x Gravitational field strength (N/kg)

What is the Gravitational field strength on Earth?

10N/kg

What is the stopping distance of a car?

The total distance travelled during the time it takes to stop in an emergency

What is the stopping distance formula?

Stopping distance = Braking distance + Thinking distance

What is the Thinking distance?

The distance travelled in the time it takes the driver to react to an emergency and prepare to stop

What are the main factors affecting thinking distance?

- The speed of the car

- The reaction time of the driver

What affects the reaction time of the driver?

- Tiredness

- Distractions

- Intoxication

What is the Braking distance?

The distance travelled under the braking force in metres

What affects the braking distance?

- Weather

- Tires

- Brakes

- The road

What is terminal velocity?

- The fastest speed that an object can reach when falling

- Reached when the upward and downward acting forces are balanced and the resultant force is 0

What forces do falling objects experience?

- Weight

- Air Resistance

Theory linked with air resistance, terminal velocity and weight

- Air resistance increases as the object's speed increases

-> Because the object collides with more air particles as it moves through the air

- Weight doesn't change

- As air resistance increases and becomes equal to the weight, the resultant force reaches 0

- The object no longer accelerates and reaches constant speed -> terminal velocity

What is Hooke's Law?

Hooke's law states that the extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality

What is the limit of proportionality? (Hooke's Law)

The point beyond which the relationship between force and extension is no longer directly proportional, varies according to the material

What does the force-extension graph look like?

Hooke's law is the linear relationship between force and extension

- ONLY REPRESENTED BY A STRAIGHT LINE

- Any material beyond its limit of proportionality will have a non-linear relationship -> represented by a curved line

What is elastic behavious?

The ability of a material to recover its original shape after the forces causing deformation have been removed

What is deformation?

A change in the original shape of an object

What are the types of deformation?

- Elastic

- Inelastic

What is Elastic Deformation?

When the object does return to its original shape after the deforming forces are removed

What is Inelastic Deformation?

When the object does not return to its original shape after the deforming forces are removing

What is density?

The mass per unit volume of a material

What is the equation for density?

Density (kg/m^3) = mass (kg) / volume (m^3)

p = m/v

What mass do objects with low density often have?

Low mass

What mass do objects with high density often have?

High mass

How does density change for a susbtance in different states?

A gas is less dense than the same substance in liquid or solid form

Volume of a sphere

4/3πr³

Volume of a cylinder

πr²h

How do you measure the density of regularly shaped objects?

- Place object on a digital balance for more accuracy + record results

- Use a ruler to measure the object's dimensions

- Repeat measurements and take the average

- Calculate volume of the object using the correct formula

- Divide mass by volume to get density

How do you measure the density of irregular shaped objects?

- Place the object on a digital balance for accuracy and record the results

- Place an empty measuring cylinder below the eureka can's spout

- Fill the eureka can with water until the water overflows + empty the measuring cylinder

- Carefully lower the object into the eureka can

- Measure the volume of displaced water in the measuring cylinder

- Repeat + take the average

- Divide mass by volume to get the density

How do you measure the density of liquids?

- Place an empty measuring cylinder on a digital balance + record results

- Fill the cylinder with liquid + record the change in mass

- Record the volume of the liquid

- Repeat + take the average

- Divide the mass by the volume to get the density

What is Pressure?

The concentration of a force

What is the equation for pressure?

Pressure (Pa) = Force (N) / Area (m²)

Explain why heels cause more damage than trainers

- Heels have a smaller area than trainers

- The smaller the area, the higher the pressure

- P = F/A

- Heels exert more pressure than trainers

- More pressure = more damage

Air Pressure: Collapsing can

- Can with a bit of water is heated up + put upside down into cold water

- Causes an implosion

- As the can + water are heated, water molecules gain enough energy to break bonds + change state

- Water vapour exerts a high pressure on the walls of the can as it is very hot -> a lot of KE + great frequency of collisions

- When placed in cold water, the vapour condenses

- Droplets don't exert as much force as the vapour did so the pressure outside the can is greater than inside the can

- Can implodes due to an imbalance of pressure + force pushing on its outside walls

Air Pressure: How does a straw work?

- There is high atmospheric pressure (100,000Pa) on the cup and a low pressure inside the mouth because the mouth acts as a vacuum

- Pressure goes from high to low when using a straw

- pressure balances out

How is pressure exerted by a gas in a sealed + fixed container?

- Molecules are in a constant state of random motion

- They collide with the walls of the container

- During the collision, there is a change in momentum + direction

- This change in momentum exerts a force because: F= M(v - u)/t

- The force exerted on the wall is equal in magnitude and acts in the opposite direction, as stated by Newton's 3rd Law

- As P = F/A, the gas exerts a pressure on the container

How does pressure change as temperature increases?

- As the temp increases, the kinetic energy of the gas increases -> speed of molecules increases

- This means that collisions occur more frequently

- There is a greater change in momentum during the collision

- This means a larger force is exerted on the container and therefore a larger pressure is exerted as the temperature increases

What is fluid pressure?

- A fluid pressure (liquid or gas) exerts a pressure at a point below the surface due to the weight of the fluid above that point

- Acts in all directions

- Acts perpendicular to the surface it is acting on

what factors affect fluid pressure?

- Depth

- Density of the Fluid

-The gravitational field strength of the planet

What is the equation for the pressure difference at different depths?

Pressure (Pa) = Height (m) x Density (kg/m^3) x Gravitational field strength (N/kg)

P = h x p x g

What is the moment of a force?

The turning effect produced when a force is exerted on an object

What is a moment?

The turning effect of a force about a pivot

What is the Moment equation?

Moment (Nm) = Force (N) x perpendicular distance from pivot (m)

In what direction should the force act to the distance from the pivot?

Force should be perpendicular to the distance from the pivot

How would increasing the distance from the pivot affect the force required?

Increasing the distance a force is applied from a pivot decreases the force required

What is the principle of moments?

- If an object is balanced, Clockwise moment = Anticlockwise moment

What is the centre of gravity?

The point through which the weight of an object acts

- For a symmetrical object of uniform density, the centre of gravity is located at the point of symmetry

How can the centre of gravity be found in an irregular object?

Through suspension

- Hang up the object

- Suspend the shape from a location near an edge, drop a plumb line and mark on the object

- Repeat from a different point not too close to the first

- The intersection of the two lines is the centre of gravity

Refraction Definition

The bending of a wave due to a change in medium when the wave moves between two mediums of different densities

What is Snell's Law?

n = sin i / sin r

- Used to calculate the refractive index of an unkown material

- The refractive index = sin i (angle of incidence) / sin r (angle of refraction)

What happens when light moves into a more dense medium?

- When light is moving from a less dense to a more dense medium, it's speed will slow down

- The light will bend towards the normal

What happens when light moves into a less dense medium?

- When light is moving from a more dense to a less dense medium, it's speed will increase

- The light will bend away from the normal

What happens when sound moves into a more dense medium?

- When sound moves from a less dense to a more dense medium, it's speed will increase

What happens when sound moves into a less dense medium?

- When sound moves from a more dense to a less dense medium, it's speed will decrease

What angle do you measure to find the angle of incidence?

The angle between the incident ray and the normal

What angle do you measure to find the angle of refraction?

The angle between the refracted ray and the normal

What is the critical angle?

The angle of incidence when the angle of refraction is 90°.

What is total internal reflection?

- Total internal reflection is where all the light is reflected inside a material.

- It happens when the angle of incidence is greater than the critical angle.

Why does total internal reflection not occur when the angle of incidence = the critical angle?

- Because light does still escape.

- Not all light is reflected

- Ergo not 'total' reflection

How do you find the refractive angle when you have the critical angle?

n = 1/sin c

- The refractive index = 1/sin c (critical angle)

Information about the electromagnetic spectrum

- A continuous range of electromagnetic waves

- A form of energy that can move through the vacuum of space

- The longest rays are the least dangerous e.g. radio waves

- The higher the frequency, the longer the waves

Electromagnetic spectrum in order from longest to shortes

- Radio waves -> REAL

- Microwaves -> MEN

- Infrared waves -> INITIATE

- Visible waves -> VERY

- Ultraviolet waves -> UNHARMONIOUS

- Xray waves -> XYLOPHONE

- Gamma ray waves -> GROUPS

Radio wave uses + dangers

Uses:

- Sound travels

- Listening to music

Dangers:

- Heating body tissues

Micro wave uses + dangers

Uses:

- Heating

- Communication

Dangers:

- Skin

- Cataracts

Infrared uses + dangers

Uses:

- Electric heaters

- Thermal cameras

Dangers:

- Heat cramps

- Exhaustion