Section 1 - Motion and forces

• What is a vector quantity?

  A quantity with a magnitude and a direction, e.g. force, velocity, displacement, weight, acceleration, momentum, etc.
• What is a scalar quantity?

  A quantity that only has a magnitude, e.g. speed, distance, mass, energy, temperature, time, etc.
• What is the difference between distance and displacement?

  Distance is how far an object's moved (scalar) and displacement (vector) measures the distance and direction in a straight line from an object's starting to finishing point.
• What is the difference between speed and velocity?

  Speed (scalar) measures how fast you're going, velocity (vector) is speed in a given direction.
• What is the equation linking speed, distance, and time?

  speed = distance/time
• What is acceleration?

  The rate of change in velocity in a certain amount of time.
• What is the equation to calculate average acceleration?

  acceleration (m/s^2) = initial velocity - final velocity (m/s)/time(s)

  a=v-u/t
• What is the equation to calculate a constant acceleration?

  final velocity^2 - initial velocity^2 = 2 x acceleration x distance

  v^2 - u^2 = 2as
• How do you find the speed on a d/t graph?

  Find the gradient at the point of the line (rise/run)
• How do you find the distance travelled on a v/t graph?

  You calculate the area under any section of the graph or all of it.
• What is the equation linking force, mass, and acceleration together?

  F = m x a
• What is Newton’s first law?

  A force is needed to change motion - if resultant force on stationary object is 0, it remains stationary.
• How does Newton’s first law describe circular motion?

  An object travelling in a circular orbit at a constant speed is constantly changing direction and changing velocity, so it is accelerating. There must be a resultant force, which acts towards the centre of the circle - a centripetal force.
• What is Newton’s third law?

  When two objects interact, the forces they exert on eachother are equal and opposite.
• What is inertia?

  The tendency for motion to remain unchanged/moving with the same velocity. An object’s inertial mass measures how hard it is to change the velocity of the object (m=F/a).
• Describe Newton’s third law in an equilibrium situation

  A man pushes against a wall and the normal contact force acts back on him. The two forces are the same size. The man pushes and the wall pushes back with an equal force.
• What is the difference between weight and mass?

  Mass is the amount of ‘stuff’ in an object and its value remains the same anywhere in the universe - scalar quantity (kg). Weight is the force acting on an object due to gravity (affected by gravitational fields) and is measured in newtons.
• What is the equation linking weight, mass and gravitational field strength?

  Weight = mass x gravitational field strength(N/Kg)/ W = mg
• What is stopping distance?

  Stopping distance is the total time taken when stopping a car - thinking distance + braking distance.
• What is the difference between thinking distance and braking distance?

  Thinking distance is the distance the car travels in the driver’s reaction time (between noticing hazard and applying breaks). Braking distance is the distance taken to stop once the brakes have been applied.
• What factors affect thinking distance

  • tiredness
  • drugs
  • alcohol
  • distractions
• What factors affect braking distance?

  • speed of car
  • icy/wet road conditions
  • worn tyres
  • worn/faulty breaks
  • mass of car
• What is momentum?

  How much ‘oomph’ any moving object has - a vector quantity, measured in kgm/s. The greater the mass or velocity, the greater the momentum.
• What equation is used to calculate momentum?

  momentum = mass x velocity

  p = mv
• What is the principle of conservation of momentum?

  In a closed system (no external forces), the total momentum before an event (eg, collision) is the same as after the event.
• What equation links force, change in momentum, and time?

  Force = final momentum - initial momentum/time

  F = mv - mu/t
• What safety features do cars have that involve momentum?

  • crumple zones - front of car crumples on impact to reduce force on driver by decreasing contact
  • air bags - inflate and act as a cushion, decreasing impact on driver’s head
  • seat belt - applies force on driver in opposite direction as the driver doesn’t stop moving when the car does.
• What is the first force acting on a falling parachutist?

  Weight
• What happens to a parachutist when only weight is acting on him?

  He accelerates due to unbalanced force
• What occurs as a parachutist travels faster?

  Air resistance increases until it is equal and opposite to his weight
• What is terminal velocity for a parachutist?

  Constant speed when forces are balanced
• What happens after a parachutist slows down post parachute opening?

  He reaches a new terminal velocity
• What does Hooke’s Law state?

  The extension of an elastic object is directly proportional to the force applied to it.
• Describe a force-extension graph.

  • Straight line = elastic deformation, will still go back to shape.
  • Point where line is not directly proportional anymore = elastic limit, the last point where spring will go back to shape.
  • Curve upwards = plastic, will no longer go back to shape.
• How can you investigate Hooke’s law?

  Practical with springs and rubber bands, measuring the relationship between the force applied and the resulting extension/compression.
• What is a moment?

  A moment is a turning effect about a pivot, produced by a force acting on an object.
• What is the equation to calculate a moment?

  Moment (Nm) = Force x Perpendicular distance
• What does the principle of moments state? 


  If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot - equillibrium.
• How can a moment be increased?

  By increasing the magnitude of the force, or increasing the length.
• Describe how to find the centre of gravity of an irregular shape

  • Hang the shape from a fixed point using a nail in a clamp stand
  • Add a plumb line (string with a mass on end) to the fixed point and mark the position
  • Hang the shape at different orientations from the same fixed point and draw on the position of the lines.
  • Where all the lines cross is the centre of gravity.