Edexcel Physics IGCSE: Forces and Motion

Study Notes

Movement and Position

Speed is the distance covered per unit of time; a changing speed indicates acceleration.
Acceleration due to gravity near Earth's surface is constant.
Velocity combines speed with direction; acceleration is the change in velocity over time: ( a = \frac{\Delta v}{t} ).
Distance is measured in meters (m), time in seconds (s), speed and velocity in meters per second (m/s), and acceleration in meters per second squared (m/s²).
Distance-time graph:
- Gradient represents velocity; a negative gradient indicates return to starting point.
- A horizontal line indicates stationary position; zero distance means back at start.
- A curved line denotes changing velocity (acceleration).
Velocity-time graph:
- Gradient indicates acceleration; negative gradient represents deceleration.
- Speed of zero indicates rest; horizontal line implies constant speed.
- Area under the line signifies distance traveled; a curved line reflects changing acceleration.

Forces, Movement, Shape, and Momentum

Difference between vectors (magnitude and direction) and scalars (magnitude only):
- Scalars: distance, speed, time, energy.
- Vectors: displacement, velocity, acceleration, force.
Forces, measured in Newtons (N), can change speed, shape, or direction. Types include gravitational and electrostatic.
Friction and air resistance impede motion, creating heat.
Resultant forces: Add forces in the same direction and subtract those in opposite directions.
Newton's Laws of Motion:
- First Law: An object remains in constant velocity unless acted upon by a resultant force.
- Second Law: ( F = ma ) (Force equals mass multiplied by acceleration).
- Third Law: For every action, there is an equal and opposite reaction.
Mass, in kilograms (kg), indicates the amount of matter; weight equals gravitational force on mass: ( W = mg ).
Gravitational field strength on Earth is approximately 10 N/kg.
Hooke's Law: For springs, ( F = kx ) (force is spring constant times extension); the gradient in a linear force-extension graph represents the spring constant ( k ).
Limit of proportionality marks the end of Hooke's Law’s applicability. Non-linear graphs indicate deformation beyond elastic limits.
Moment (turning effect of a force) is calculated as ( \text{moment} = \text{force} \times \text{perpendicular distance} ) and is measured in Newton metres (Nm).
An object is in equilibrium when clockwise moments equal anticlockwise moments, resulting in no resultant force.
Location of an object on a beam affects the upward forces at supports; the closer the object to a support, the greater the force at that support.
Momentum ( p = mv ) (mass times velocity) is measured in kilogram meters per second (kgm/s).
Force relates to change in momentum over time: ( F = \frac{\Delta p}{t} ); reduced force results by increasing time to rest in crash scenarios.
Safety features like seatbelts lengthen the time taken to stop, thus reducing force experienced.