forces and motion chapter 1-3

Chapter 1: Speed, Velocity and Distance 

Distance 

  • Total path travelled.  

  • Scalar quantity (has size only).  

  • Unit: metres (m)  

Displacement 

  • Straight-line distance from the start to the finish with direction.  

  • Vector quantity.  

  • Unit: metres (m)  

Example: 

  • Walk 5 m east, then 5 m west.  

  • Distance = 10 m  

  • Displacement = 0 m 

 

 

Speed is how fast and object moves  

 

Formula 

Speed = Distance ÷ Time 

v = d ÷ t 

Units: 

  • m/s  

  • km/h  

Example 

Distance = 200 m 

Time = 20 s 

Speed = 200 ÷ 20 = 10 m/s 

 

 

Speed-Time Graphs 

  • Horizontal line = constant speed  

  • Upward slope = accelerating  

  • Downward slope = slowing down  

  • Horizontal line at zero = stationary 

 Newtons laws:  

 

  1. An object remains at rest or moves at constant velocity unless acted upon by a resultant force. 

  2. Examples: 

  3. Seat belts stop passengers moving forwards when a car brakes.  

  4. A football stays still until kicked. 

 

  1. F=MXA  

  • Formula 

Force = Mass × Acceleration 

F = ma 

Where: 

  • F = force (N)  

  • m = mass (kg)  

  • a = acceleration (m/s²)  

Example 

Mass = 5 kg 

Acceleration = 3 m/s² 

Force = 5 × 3 

= 15 N 

 

  1. For every action, there is an equal and opposite reaction. 

 Examples: 

Rocket pushes gas down → Gas pushes rocket up.  

You push on the ground → The ground pushes back on you. 

 Chapter 2: Acelration 

 

Acceleration is the rate of change of velocity. 

Formula 

Acceleration = Change in velocity ÷ Time 

a = (v − u) ÷ t 

Where: 

  • u = initial velocity  

  • v = final velocity  

  • t = time  

Example 

Car speeds up from 5 m/s to 25 m/s in 10 s. 

Acceleration = (25 − 5) ÷ 10 

= 2 m/s² 

 

Deceleration 

Negative acceleration. 

Occurs when an object slows down. 

 

 Chapter 3:Forces 

 

A force is a push or pull. 

Unit = Newton (N) 

Examples: 

  • Gravity  

  • Friction  

  • Air resistance  

  • Tension  

  • Normal contact force  

  • Upthrust  

 
 

Balanced Forces 

  • Equal size  

  • Opposite direction  

Result: 

  • Object stays still or  

  • Moves at constant speed  

 
 

Unbalanced Forces 

  • One force is bigger  

Result: 

  • Object accelerates  

  • Slows down  

  • Changes direction  

 

 

 

  • Weight 

Weight is the force of gravity acting on an object. 

 

Formula 

Weight = Mass × Gravitational field strength 

W = mg 

Where: 

  • W = weight (N)  

  • m = mass (kg)  

  • g = 9.8 N/kg (or 10 N/kg in many exam questions)  

Example: 

Mass = 8 kg 

Weight = 8 × 10 = 80 N