Vector quantities
have magnitude and direction
Examples of vector quantities
force, velocity, momentum, acceleration
Scalar quantities
Only have magnitude and no direction
Examples of scalar quantities
speed, distance, time
Vectors
represented by an arrow - the length of the arrow shows the magnitude. The direction of the arrow shows the direction of the quantity
A force is
a push or pull on an object that is caused by it interacting with something
when two objects are touching for the force to act, its a ....
contact force
examples of contact forces
friction, air resistance, tension in ropes. etc
If the objects do not need to be touching for the force to act, the force is a ......
non contact force
examples of non contact forces
magnetic force and gravitational force
Two effects of gravity
makes all things fall towards the ground
gives everything a weight
What is mass?
The amount of material an object is made of It is the same value everywhere Measured using a mass balance
What is weight?
The force acting on an object due to gravity It depends on the strength of the gravitational field at the location of the object Measured using a calibrated spring balance - newtonmeter
Equation for Weight
Weight (N) = Mass (kg) x Gravitational Field Strength (N/kg) W=mg
What is weight directly proportional to?
mass
What are free body diagrams?
Diagrams that show all the forces acting on an object
What is the resultant force?
The single force that replaces multiple forces acting at a single point
How is work done?
When a force moves an object through a distance, energy is transferred and work is done on the object
Equation for 'Work Done'
Work done (J) = Force (N) x Distance (m) W=Fs
What is 1J equal to?
1Nm
If all the forces acting on an object combine to give a resultant force of zero then the object is in ?
equilibrium
What could happen when you apply a force to an object?
It may stretch, compress or bend
What happens when an object is elastically deformed
The object can go back to its original shape and length after the force has been removed
What happens when an object is inelastically deformed?
The object won't return to its original shape and length after the force has been removed
Equation for Force 1
Force (N) = Spring Constant (N/m) x Extension (m) F=ke
Extension is directly proportional to? (Hooke's Law)
The force applied F∝e
What is the limit of proportionality?
The point at which extension is no longer directly proportional to force
What is momentum?
Momentum is the product of mass and velocity. Momentum is also a vector quantity – this means it has both a magnitude and an associated direction
Equation for Elastic potential energy
Elastic potential energy (J) = 1/2 x Spring Constant (N/m) x extension^2 (m) Ee = 1/2Ke^2
What is displacement?
It measures the distance and direction in a straight line from an object's starting point to its finishing point
What is velocity?
Speed (how fast you're going) in a given direction
Equation for Speed
Distance Travelled (m) = Speed (m/s) x Time (s) s=vt
typical speeds
typical speed of a person walking 1.5m/s typical speed of a person running 3m/s Typical speed of a person cycling 6m/s what is the typical speed of a car 25m/s Typical speed of a train 55m/s Typical speed of a plane 250m/s
What factors affect speed?
Fitness of the person Age of the person Distance travelled Terrain Climate Gender of the person
What factors affect wind speed?
Temperature Atmospheric pressure Any large buildings or structures nearby e.g. forests reduce wind speed travelling through them
Acceleration
change in velocity in a certain amount of time
Equation for Acceleration
Acceleration (m/s²) = Change in Velocity (m/s) / Time (s) a=Δv/t
What is deceleration?
Negative acceleration - when something slows down, the change in velocity is negative
What is constant acceleration?
Uniform acceleration - acceleration due to gravity is uniform for objects in free fall
Equation for Uniform Acceleration
Final velocity² (m/s) - Initial velocity² (m/s) = 2 x Acceleration (m/s²) x Distance (m) v²-u²=2as
Distance-Time Graphs - Features
Gradient = speed
Flat sections = object is stationary
Straight uphill sections = object is travelling at a steady speed
Curves = object is accelerating or decelerating
Steepening curve = object is speeding up
Levelling off curve = object is slowing down
Velocity-Time Graphs - Features
Gradient = acceleration
Flat sections = object is travelling at a steady speed
Uphill sections = object is accelerating
Downhill sections = object is decelerating
Curves = object is changing acceleration The steeper the graph, the greater the acceleration or deceleration
What does friction do?
It causes objects to slow down when they rub against another surface
What is drag?
The resistance you get in a fluid Air resistance is a type of drag
How do you reduce drag?
Keep the shape of an object streamlined
process of a falling object
When a falling object first sets off, the force of gravity is much more than the frictional force slowing it down, therefore the object accelerates
As the speed increases, the friction builds up
The acceleration is gradually reduced until eventually, the friction force is equal to the accelerating force - the resultant force is 0
At this point, it will have reached maximum speed or terminal velocity and will fall at a steady speed
What determines the terminal velocity?
The terminal velocity of any object is determined by its drag in comparison to its weight
In the last few metres of his descent during the parachute stage, the person travels at a terminal velocity. Explain why (2)
Because the drag had the same force on the parachuter as the weight
weight pushes him down
Drag/air resisance keeps him. Hes reached terminal velocity (2)
What is the tendency for objects to continue at the same speed in the same direction called?
Inertia
Newton's First Law - Law of Inertia
If the resultant force on a stationary object is zero, the object will remain stationary If the resultant force on a moving object is zero, it will just carry on moving at the same velocity
Newton's Second Law
Force ∝ Acceleration Acceleration is inversely proportional to the mass of an object
Equation for resultant force
Resultant Force (N) = mass (Kg) x acceleration (M/s^2) F=ma
Newtons third Law
When two objects interact, the forces they exert on each other are equal and opposite An action always has an equal and opposite reaction
Explain why you don't move when you lean on a wall, even though you are exerting a force (3)
When you lean on a wall, you exert a force on the wall. Due to Newtons third Law, the wall also exerts an equal but opposite force back onto you.(1) You also exert a force on the ground and the ground exerts a force on you(1)The resultant force is zero, so you remain stationary (1)
Investigating effect of mass
Add masses to the trolley one at a time to increase the mass of the system 2)Record average acceleration for each mass To reduce the effect of friction use an air track.
Investigating acceleration
Set up a trolley so it holds a piece of card that will interrupt the signal on the light gate twice.
This will measure acceleration.
Using a light measure the first and second point it passes. Work out an average acceleration. To reduce the effect of friction use an air track.
investigating effect of force
Keep total mass of the system the same but the change the mass on hook
Start with all the masses onto trolley
Transfer the hooks one at a time to the hook, to increase the accelerating force
The mass of the system stays the same as you're transferring the masses from one part of the system to another (the hook)
Record the average acceleration for each force To reduce the effect of friction use an air track.
What is the thinking distance?
How far the car travels during the driver's reaction time
What is the braking distance?
The distance taken to stop under the braking force
What is stopping distance?
The distance it takes for a car to stop in an emergency
Equation for Stopping Distance
Stopping Distance = Thinking Distance + Braking Distance
What is thinking distance affected by?
Speed - the faster you're going, the further you'll travel during your reaction time
Your reaction time - the longer it is, the longer your thinking distance
Alcohol
Drugs
Sleep deprivation
Distractions
What is braking distance affected by?
Speed - the faster a vehicle travels, the longer it takes to stop
Weather/Road surface - if it's wet or icy, there is less grip (and less friction) between a vehicle's tyres and the road, which can cause tyres to skid
Condition of tyres - if the tyres are bald, then they cannot get rid of water in wet conditions, thus leading to skidding on top of the water
Quality of brakes - if brakes are worn or faulty, they won't be able to apply as much force as well-maintained brakes, which could be dangerous when wanting to brake hard
What happens when a vehicle is going really fast?
It has more energy in its kinetic energy stores, so the more work needs to be done to stop it - a greater braking force will be needed to make the vehicle stop within a certain distance, therefore the deceleration will be larger The larger the deceleration, the more dangerous it will be as the brakes could overheat or cause the vehicle to skid
At one time in the investigation, the cyclist was distracted. The distraction increased the stopping distance of the bike but did not affect the braking distance Explain why the stopping distance increased
The cyclist's reaction time increased (1) The thinking distance increased (1) Stopping distance is thinking distance plus braking distance (1)
Describe how Newtons third law applies to the forces between the bike and the trailer
The forces of the bike on the trailer and the trailer on the bike are equal in size and opposite in direction
Typical reaction time
in between 0.2 - 0.9
Measure reaction time :
Ruler drop test
Computer based experiments
Marks reaction time is tested using the ruler drop test. He is tested early in the afternoon and at night. In the afternoon, he catches the ruler after it has fallen a distance of 16.2cm. At night, he catches the ruler after it has fallen 18.5cm. a) Calculate Mark's reaction time in the afternoon. Give your answer to 2 significant figures
v^2 - u^2 = 2as v^2 = 2 x 9.8 x 0.162 + 0 = 3.1752 (1) v= √3.1752 = 1.781 m/s (1) a = Δv/t t = Δv / a = 1.781 / 9.8 = 0.181 s (1) = 0.18 (to s.f)
What is momentum?
How much 'oomph' an object has All moving objects have it The momentum of one thing is always equal to the momentum of another thing e.g. a skateboarder has the same momentum as the skateboard
Equation for Momentum
Momentum (kg m/s) = mass (kg) x velocity (m/s) p=mv
What is the conservation of momentum?
In a closed system, the total momentum before an event is the same as after the event
Wave
something that transfers energy from one place to another
transverse waves
The vibrations are perpendicular (at right angles) to the direction of energy transfer
direction of energy transfer is sideways - but oscillations are up and down
examples of transverse waves
electromagnetic waves e.g light
Ripples and waves in water
longitudinal waves
The oscillations are parallel to the direction of energy transfer
examples of longitudinal waves
sound waves e.g ultrasound
Explain the differences between the properties of the sound waves produced by the motor and the water waves in the ripple tank
Sound waves are longitudinal, in longitudinal waves the oscillations are parallel to the direction of energy transfer
Water waves are transverse. In transverse waves, the oscillations are perpendicular to the direction of energy transfer
Explain why the light is refracted
Because light travels more slowly (in the glass block than in the air) so it changes direction
Compression
regions where the air particles are very close together
Rarefaction
regions where the air particles are spaced out
wave speed equation
wave speed (m/s) = frequency (H/z) x wavelength (m) V = f λ
amplitude
The amplitude of a wave is the greatest distance a point on the wave moves from its undisturbed postion
wavelength
The wavelength of a wave is the distance from a point on one way to the equivalent point on the adjacent wave
measure wavelength on longitudinal waves
measure from one compression to the next compression or from one rarefaction to the next rarefaction
frequency
the number of waves passing a point each second 1 Hz = 1 wave per second
period
time (in seconds) for one wave to pass a point
equation for period
period = 1/frequency (H/z)
What is the speed of sound in air?
330m/s
measuring the speed of water ripples practical
use signal generator attached to dipper of ripple tank - can create water waves at set frequency use strobe light to see wave crests on a screen below the tank increase frequency of strobe light until wave pattern on the screen appears to freeze and stop moving. Distance between each shadow line is equal to one wavelength Measure the distance between shadow lines that are 10 wavelength apart, then divide this distance by 10 to find the average wavelength use V = f λ
strobe is effective because
it allows you to measure a still pattern instead of a constantly moving one
required practical: waves in a solid
Turn on the signal generator and vibration transducer. String will start to vibrate
Adjust the frequency of the signal generator until there's a clear wave on the string
Measure the wavelength of these waves by measuring the lengths of 5 half wavelengths in one go, then divide to get the mean half wavelength, then double this to get a full wavelength
Frequency of the wave is whatever the signal generator is set to
use V = f λ to find the speed of the wave
3 things that could happen when a wave meets a boundary between two materials :
The wave is transmitted through the material - carries on travelling
The wave is absorbed by the material
The wave is reflected - 'sent back' - this is how echoes are produced
Rule for all reflected waves
Angle of incidence = angle of reflection
What is the angle of incidence?
The angle between the incoming wave and the normal
What is the angle of reflection?
the angle between the refracted wave and the normal
What is the normal?
An imaginary line that's perpendicular to the surface at the point of incidence
Length of a radio wave
1m-10⁴m
Length of a microwave
10⁻²m
Length of a infrared wave
10⁻⁵m