Paper 2

• 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
• 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
• 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
• What is the limit of proportionality?


  The point at which extension is no longer directly proportional to force

  
• Practical: Investigating the link between force and extension

  - First, measure the original length of the spring using a milimetre ruler

  - Next, add different masses on the spring and measure the length of the spring in each case.

  - The extension = change in length

  - Repeat this process until you have enough measurements ( no fewer than 6)

  - Plot a graph with extension of the spring on the x axis and force on the y axis.

  - The graph will only start to curve if you exceed the limit of proportionality
• 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
• 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
• 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

  1) Gradient = speed

  2) Flat sections = object is stationary

  3) Straight uphill sections = object is travelling at a steady speed

  4) Curves = object is accelerating or decelerating

  5) Steepening curve = object is speeding up

  6) Levelling off curve = object is slowing down

  
• Velocity-Time Graphs - Features

  1) Gradient = acceleration

  2) Flat sections = object is travelling at a steady speed

  3) Uphill sections = object is accelerating

  4) Downhill sections = object is decelerating

  5) 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

  1) 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

  2) As the speed increases, the friction builds up

  3) The acceleration is gradually reduced until eventually, the friction force is equal to the accelerating force - the resultant force is 0

  4) 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