Motion, Forces and Energy

You will be able to

• Explain the difference between a scalar and a vector quantity, with examples.
• Determine the resultant of two perpendicular vectors by scale drawing, using a stated scale and a protractor.
• Calculate the magnitude of the resultant with Pythagoras and its direction with tan θ.

You will be able to

• Sketch and interpret distance–time and speed–time graphs for rest, constant speed, acceleration and deceleration.
• Determine speed from the gradient of a distance–time graph and acceleration from the gradient of a speed–time graph.
• Calculate the distance travelled from the area under a speed–time graph.

You will be able to

• Describe how air resistance changes with speed and explain why a falling object reaches terminal velocity.
• Calculate the acceleration from the resultant force using a = F ÷ m.
• Sketch and interpret the speed–time graph of a skydiver before and after the parachute opens.

You will be able to

• Define thinking distance, braking distance and stopping distance, and calculate each for a given speed.
• Describe the factors that affect thinking distance and those that affect braking distance.
• Determine the stopping distance from the area under a speed–time graph.

You will be able to

• Plot a load–extension graph from recorded readings and determine the spring constant from its gradient.
• Identify the limit of proportionality as the point where the graph stops being a straight line through the origin.
• Describe what happens to a spring loaded beyond its elastic limit.

You will be able to

• Calculate the moment of a force as force × perpendicular distance from the pivot, in N m.
• Apply the principle of moments to find an unknown force or distance on a balanced beam.
• Explain that an object is in equilibrium only when there is no resultant force and no resultant moment.

You will be able to

• Calculate momentum p = mv, treating velocity to the left as negative.
• Apply the conservation of momentum to predict the velocity after a collision or explosion.
• Explain, using impulse = FΔt = Δp, why a longer contact time reduces the force in a crash.

You will be able to

• Calculate changes in gravitational potential energy (ΔEp = mgΔh) and kinetic energy (Ek = ½mv²).
• Describe energy transfers between stores and explain why the total energy stays constant.
• Calculate the efficiency of a transfer as useful energy output ÷ total energy input.

You will be able to

• Calculate the pressure change in a liquid using Δp = ρgΔh.
• Describe how liquid pressure depends on depth and density and acts equally in all directions at a point.
• Calculate pressure as force ÷ area and explain why a smaller area gives a greater pressure.