1 - FORCES AND MOTION 

Stopping distances - 

Stopping distance - time between first spotting a hazard and the car coming to a complete stop 

Thinking distance - time between driving noticing hazard and applying brakes 

Affected by: 

• How fast you're going 
• How aware the driver is - eg: tiredness, drugs, alcohol, age, inexperience 

Braking distance - distance the car travels during deceleration while brakes are being applied 

Affected by: 

• How fast you're going 
• Mass of vehicle (the larger the mass, the longer it takes to stop)
• Quality of brakes 
• Grip - road surface, weather conditions, tyres 

1 - FORCES AND MOTION 

The 3 laws of motion - 

1 - Balanced forces mean no change in velocity

• If the forces are balanced, on a non-moving object, it will just stay still 
• If the object is already moving, it will continue at the same velocity 

- a train going at a constant velocity has all the forces acting on it balanced - steady speed = no resultant force 

2 - A resultant force means acceleration 

• Unbalanced force = object accelerates in that direction 

- acceleration =starting, speeding up, stopping, slowing down, changing direction - on a force diagram the arrows will be unequal 
- the bigger the force, the greater the acceleration/deceleration 
- the bigger the mass, the smaller the acceleration 

Unbalanced force (resultant force) - 
Resultant force = mass x acceleration (F = ma)
Acceleration = resultant force/mass (a = F/m)


3 - Reaction forces 

•  If object A exerts a force on object B, object B exerts the exact opposite force on object 

- same sized forces in opposite directions 
- movement depends on mass etc. 
- eg: swimming 

1 - FORCES AND MOTION 

Motion experiment - 

1. Set up apparatus like picture (however, include a light gate at the start line, one at the base of the slope and one t the end of a long flat strip after) 
2. Mark start line 
3. Measure distance between each light gate 
4. Allow car to roll down from starting point (ensure light gates are linked to computer data software)
5. Repeat for average time taken for the car to reach each light gate 
6. Find average speed (average time taken between gates / distance between gates) 

Possible alterations - 

• Mass - put weights on car to see effect 
• Friction - place different materials on ramp (eg: carpet) 
• Acceleration (due to gravity) - move start line higher or lower, will affect average speed between gates
• Speed - change angle of ramp 
• Size/shape/weight of car - use different cars (eg: streamlined)

1 - FORCES AND MOTION 

Forces and friction - 

• Gravity/weight - straight downwards 
• Reaction force - from surface, usually straight upwards 
• Electrostatic force - between 2 charged objects (direction depends on type of charge, eg: repel, attract etc) 
• Thrust/push/pull - eg: due to engine or rocket speeding something up 
• Drag/air resistance/friction - slowing object down 
• Lift - eg: due to aeroplane wing 
• Tension - eg: in rope or cable

 Friction - 

• Opposes motion (unless in space)
• To stay at a a steady speed, there needs to be a driving force to counteract friction

1. Static friction - between solid surfaces that are gripping 
2. Sliding friction - between solid surfaces that are sliding past eachother (lubricant between surfaces eg: oil/grease) 
3. Resistance/drag - can be reduced by making object streamlined, lowers top speed of an object (eg: parachute)

1 - FORCES AND MOTION 

Mass, weight and gravity - 

Gravity - force of attraction between all masses 

1. Surface of a planet - all things accelerate towards ground (eg: at 10m/s^2 on Earth) 

2. Gives everything a weight 

3. Keeps planets, moons and satellites in orbit

Mass -  

• Amount of 'stuff' in an object 
• Same value anywhere in universe 
• Same mass on Earth or moon/anywhere 
• Measured in kilograms (kg)

Weight - 

• Caused by pull of gravity 
• The force of gravity pulling object towards centre of Earth 
• Changes in different places depending on gravitational field strength (eg: 10N on Earth, 1.6N on moon) 
• Measured in newtons (N) 

 

Weight (N) = mass (kg) x gravitational field strength (N/kg)

1 - FORCES AND MOTION 

Distance-time and velocity-time graphs - 

Distance-time graphs - 

• Gradient = speed 
• Flat sections = stopped 
• Steeper = faster 
• Downhill = other direction towards starting point 
• Curves = acceleration/deceleration 
• Steepening curve (increasing gradient) = speeding up
• Levelling off curve (decreasing gradient) = slowing down

eg: 
Speed = gradient = vertical/horizontal 
                = 2/1 = 2m/s  

Velocity-time graphs - 

• Gradient = acceleration 
• Flat sections = steady speed 
• Steeper = greater acceleration/deceleration
• Uphill (/) = acceleration 
• Downhill (\) = deceleration 
• Area under any section of graph = distance travelled in that time interval
• Curve = changing acceleration 

 eg: 
Acceleration = gradient = vertical/horizontal 
                    = 2/1 = 2 m/s^2 (squared) 
Speed = value from velocity axis 
Distance travelled = area under graph

1 - FORCES AND MOTION 

Velocity and Acceleration -

Speed - how fast you're going (m/s)

Velocity - speed with a direction (m/s and direction)

Average speed = distance moved / time taken




Acceleration - how quickly velocity is changing (eg: change in speed, change in direction) (m/s squared)




Acceleration = change in velocity / time taken