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Forces and motion
This topic connects forces to motion through distance-time graphs, velocity-time graphs, acceleration, resultant force and Newton's laws.
85
Objectives
425
Flashcards
425
Questions
90 min
Study time
AQAGCSEPhysicsForces
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85 objective pages available
Distance, displacement, speed and velocity12 objectives
- Define distance as how far an object moves regardless of direction.
- Define displacement as distance moved in a particular direction from a starting point.
- Define speed as distance travelled per unit time.
- Define velocity as speed in a given direction.
- Use the equation distance travelled = speed x time.
- Calculate speed from distance and time.
- Calculate distance from speed and time.
- Calculate time from distance and speed.
- Convert between metres per second and kilometres per hour where appropriate.
- Distinguish average speed from instantaneous speed.
- Explain why velocity can change if direction changes even when speed is constant.
- Apply MS 3b and MS 3c skills when using speed, distance and time equations.
Distance-time graphs10 objectives
- Interpret a horizontal line on a distance-time graph as an object being stationary.
- Interpret a straight sloping line on a distance-time graph as constant speed.
- Interpret a steeper gradient as a greater speed.
- Calculate speed from the gradient of a distance-time graph.
- Draw a tangent to estimate speed at a point on a curved distance-time graph.
- Interpret a curved distance-time graph as changing speed.
- Describe motion from a distance-time graph in words.
- Sketch distance-time graphs for simple journeys.
- Identify units on distance and time axes.
- Apply MS 4a, MS 4b and MS 4c skills when interpreting graph gradients.
Acceleration10 objectives
- Define acceleration as the rate of change of velocity.
- Use the equation acceleration = change in velocity divided by time taken.
- Calculate acceleration from change in velocity and time.
- Calculate change in velocity from acceleration and time.
- Calculate time from change in velocity and acceleration.
- State that acceleration is measured in metres per second squared.
- Interpret positive acceleration as increasing velocity in the chosen direction.
- Interpret negative acceleration or deceleration as decreasing velocity in the chosen direction.
- Explain that an object can accelerate when its direction changes.
- Apply MS 3b and MS 3c skills when using acceleration equations.
Velocity-time graphs10 objectives
- Interpret a horizontal line on a velocity-time graph as constant velocity.
- Interpret a straight sloping line on a velocity-time graph as constant acceleration.
- Calculate acceleration from the gradient of a velocity-time graph.
- Interpret a negative gradient as deceleration or acceleration in the opposite direction.
- Calculate distance travelled from the area under a velocity-time graph.
- Interpret triangular and rectangular areas under velocity-time graphs.
- Sketch velocity-time graphs for simple motion.
- Distinguish distance-time graphs from velocity-time graphs.
- Use graph axes and units correctly when calculating gradient or area.
- Apply MS 4a, MS 4b and MS 4c skills when analysing velocity-time graphs.
Uniform acceleration (HT only)9 objectives
- (HT only) State that the equation final velocity squared minus initial velocity squared equals two times acceleration times distance applies to uniform acceleration.
- (HT only) Use v^2 - u^2 = 2as to calculate final velocity when initial velocity, acceleration and distance are known.
- (HT only) Use v^2 - u^2 = 2as to calculate initial velocity when final velocity, acceleration and distance are known.
- (HT only) Use v^2 - u^2 = 2as to calculate acceleration when velocities and distance are known.
- (HT only) Use v^2 - u^2 = 2as to calculate distance when velocities and acceleration are known.
- (HT only) Identify when uniform acceleration is required before using the equation.
- (HT only) Square and square-root velocity values correctly in calculations.
- (HT only) Use consistent units for velocity, acceleration and distance.
- (HT only) Apply MS 3b and MS 3c skills when rearranging v^2 - u^2 = 2as.
Newton's laws of motion13 objectives
- State Newton's first law in terms of motion remaining unchanged when resultant force is zero.
- Explain that an object at rest remains at rest when resultant force is zero.
- Explain that an object moving at constant velocity continues at constant velocity when resultant force is zero.
- Explain that a non-zero resultant force causes acceleration.
- Use Newton's second law as resultant force = mass x acceleration.
- Calculate resultant force from mass and acceleration.
- Calculate mass from resultant force and acceleration.
- Calculate acceleration from resultant force and mass.
- Interpret inertial mass as a measure of how difficult it is to change an object's velocity.
- Explain Newton's third law as interacting objects exert equal and opposite forces on each other.
- Identify action-reaction force pairs acting on different objects.
- Distinguish Newton's third-law pairs from balanced forces acting on one object.
- Apply MS 3b and MS 3c skills when using F = ma.
Required practical: acceleration10 objectives
- Describe how to investigate the effect of changing force on the acceleration of a trolley.
- Describe how to investigate the effect of changing mass on the acceleration of a trolley.
- Identify control variables in an acceleration investigation.
- Measure time and distance to calculate acceleration.
- Use light gates, data loggers or ticker timers to collect motion data.
- Plot suitable graphs to investigate relationships involving force, mass and acceleration.
- Explain why repeated measurements improve reliability.
- Identify sources of uncertainty in an acceleration practical.
- Interpret practical data in terms of Newton's second law.
- Apply WS and MS skills when processing acceleration practical data.
Stopping distances and safety11 objectives
- Define stopping distance as thinking distance plus braking distance.
- Define thinking distance as the distance travelled during the driver's reaction time.
- Define braking distance as the distance travelled while the brakes are applied.
- Explain how increased speed affects thinking distance.
- Explain how increased speed affects braking distance.
- Explain how tiredness, alcohol, drugs and distractions can increase reaction time.
- Explain how poor road conditions can increase braking distance.
- Explain how poor tyre or brake condition can increase braking distance.
- Interpret data or graphs about stopping distances.
- Explain why faster vehicles require greater stopping distances.
- Link braking distance to work done by braking forces and energy transfer.
Key terms
DistanceDirectiondisplacementdistanceSpeedvelocityspeedmetrekilometre per houraverage speedinstantaneous speedVelocity
Exam tips
- Remember the definition of distance: When answering questions, state that distance is the total length travelled by an object, irrespective of direction, and emphasise it is a scalar quantity.
- Understand Displacement: Use the named force or motion quantity when you remember that displacement is not just about how far you travel, but also the direction from your starting point. Link your answer to Distance, displacement, speed and velocity and keep distance and displacement separate.
Common mistakes
- Confusing Distance with Displacement: Emphasize that distance is a scalar quantity representing how far an object has traveled, regardless of direction, while displacement is a vector quantity that includes both distance and direction from the starting point.
- Confusing Distance and Displacement: Emphasize that displacement is specifically the straight-line distance from the starting point to the final position, including direction.
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