PHYSICS UNIT 2 Physics P2 for GCSE Additional Science or GCSE Physics

AQA GCSE Science PHYSICS 2 Unit P2.1 Forces and their effects

• Appreciate that forces can cause changes to the shape or motion of an object.

• Not only can objects can move in a straight line at a constant speed but they can also change their speed and/ or direction (accelerate or decelerate).

• Be able to use/produce graphs can help us to describe the movement of an object.

• These may be distance-time graphs or velocity-time graphs.

• You should be able to use their skills, knowledge and understanding to:

  • interpret data from tables and graphs relating to speed, velocity and acceleration

  • evaluate the effects of alcohol and drugs on stopping distances

  • evaluate how the shape and power of a vehicle can be altered to increase the vehicle’s top speed

  • draw and interpret velocity-time graphs for objects that reach terminal velocity, including a consideration of the forces acting on the object.

AQA GCSE Science PHYSICS Unit P2.1.1 Resultant forces

• a) Know and understand that whenever two objects interact, the forces they exert on each other are equal and opposite.

• b) Know and understand that a number of forces acting at a point may be replaced by a single force that has the same effect on the motion as the original forces all acting together.

  • Know that this single force is called the resultant force.

• c) Know and understand that a resultant force acting on an object may cause a change in its state of rest or motion.

  • You should be able to determine the resultant of opposite or parallel forces acting in a straight line.

• d) Know and understand that if the resultant force acting on a stationary object is:

  • zero, the object will remain stationary

  • not zero, the object will accelerate in the direction of the resultant force.

• e) Know and understand that if the resultant force acting on a moving object is:

  • zero, the object will continue to move at the same speed and in the same direction

  • not zero, the object will accelerate in the direction of the resultant force.

AQA GCSE Science PHYSICS Unit P2.1.2 Forces and motion

• a) Know that the acceleration of an object is determined by the resultant force acting on the object and the mass of the object.

  • Be able to use the equation:

  • a = F / M   or   F = m x a   (F = ma)

  • a = acceleration in metres per second squared, m/s²

  • F = the resultant force in newtons, N

  • m = mass in kilograms, kg

• b) Know and understand that the gradient of a distance–time graph represents speed.

  • You should be able to construct distance–time graphs for an object moving in a straight line when the body is stationary or moving with a constant speed.

• c) HT only: You should be able to calculate the speed of an object from the gradient of a distance–time graph.

• d) Know that the velocity of an object is its speed in a given direction.

• e) Know and understand that the acceleration of an object is given by the equation:

  • Be able to use the equation:

  • a = (v – u) / t

  • a is the acceleration in metres per second squared, m/s²

  • v is the final velocity in metres per second, m/s

  • u is the initial velocity in metres per second, m/s

  • t is the time taken in seconds, s

• f) Know and understand that the gradient of a velocity–time graph represents acceleration.

• g) HT only:  Be able to calculate the acceleration of an object from the gradient of a velocity–time graph.

• h) HT only: Be able to calculate the distance travelled by an object from a velocity–time graph.

AQA GCSE Science PHYSICS Unit P2.1.3 Forces and braking

• a) Know and understand that when a vehicle travels at a steady speed the resistive forces balance the driving force.

  • You should know and understand that most of the resistive forces are caused by air resistance.

• b) Know and understand that the greater the speed of a vehicle the greater the braking force needed to stop it in a certain distance.

  • You should know and understand that for a given braking force the greater the speed, the greater the stopping distance.

• c) Know and understand that the  stopping distance of a vehicle is the sum of the distance the vehicle travels during the driver’s reaction time (thinking distance) and the distance it travels under the braking force (braking distance).

• d) Know and understand that the a driver’s reaction time can be affected by tiredness, drugs and alcohol.

  • You should appreciate that distractions may affect a driver’s ability to react.

• e) Know and understand that when the brakes of a vehicle are applied, work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of the brakes increase.

• f) Know and understand that the a vehicle’s braking distance can be affected by adverse road and weather conditions and poor condition of the vehicle.

  • You should understand that ‘adverse road conditions’ includes wet or icy conditions.

  • Poor condition of the car is limited to the car’s brakes or tyres.

AQA GCSE Science PHYSICS Unit P2.1.4 Forces and terminal velocity

• a) Know and understand that the faster an object moves through a fluid the greater the frictional force that acts on it.

• b) Know and understand that an object falling through a fluid will initially accelerate due to the force of gravity.

  • You should understand that eventually the resultant force will be zero and the object will move at its terminal velocity (steady speed).

  • You should understand why the use of a parachute reduces the parachutist’s terminal velocity.

• c) Be able to draw and interpret velocity-time graphs for objects that reach terminal velocity, including a consideration of the forces acting on the object.

• d) Be able to calculate the weight of an object using the force exerted on it by a gravitational force:

  • Be able to use the equation:

  • W = m x g    (W = mg)

  • W = the weight of the object in newtons, N

  • m is the mass in kilograms of the object, kg

  • g is the gravitational field strength in newtons per kilogram, N/kg

AQA GCSE Science PHYSICS Unit P2.1.5 Forces and elasticity

• a) Know and understand that a force acting on an object may cause a change in shape of the object.

• b) Know and understand that a force applied to an elastic object such as a spring will result in the object stretching and storing elastic potential energy.

  • Calculation of the energy stored when stretching an elastic material is not required.

• c) Know and understand that for an object that is able to recover its original shape, elastic potential energy is stored in the object when work is done on the object to change its shape.

• d) Know and understand that the extension of an elastic object is directly proportional to the force applied, provided that the limit of proportionality is not exceeded:

  • Be able to use the equation:

  • F = k x e   (F = ke)

  • F is the force in newtons, N

  • k is the spring constant in newtons per metre, N/m

  • e is the extension in metres, m

• Practical work in unit 2.1 to help develop your skills and understanding may have included the following:

  • dropping a penny and a feather in a vacuum and through the air to show the effect of air resistance

  • planning and carrying out an investigation into Hooke’s Law

  • catapult practicals to compare stored energy

  • measurement of acceleration of trolleys using known forces and masses

  • timing objects falling through a liquid, eg wallpaper paste or glycerine, using light gates or stop clocks

  • planning and carrying out an investigation to measure the effects of air resistance on parachutes, paper spinners, cones or bun cases

  • measuring reaction time with and without distractions, eg iPod off and then on.