Edexcel Physics IGCSE: Forces and Motion

Study Notes

Speed is defined as the distance travelled per unit time.
Acceleration occurs when speed changes; free fall acceleration near Earth is constant.
Velocity includes direction in addition to speed.
Acceleration formula: ( a = \frac{v - u}{t} ) where ( v ) is final velocity, ( u ) is initial velocity, and ( t ) is time.
Distance-time graphs show that:
- Gradient represents velocity.
- A negative gradient indicates returning to the start.
- A horizontal line indicates stationary motion.
- A curved line suggests changing velocity.
Velocity-time graphs show that:
- Gradient represents acceleration.
- A negative gradient indicates deceleration.
- A horizontal line signifies constant speed.
- The area under the line represents the distance travelled.

Vectors have both magnitude and direction, while scalars have only magnitude.
Examples include:
- Scalars: distance, speed, time, energy.
- Vectors: displacement, velocity, acceleration, force.
Forces can change an object's speed, shape, or direction, measured in Newtons (N).
Friction impedes motion between surfaces and causes heating; air resistance is a type of friction.
Resultant forces are found by adding forces in the same direction and subtracting opposites.
Newton's Laws of Motion:
- First Law: An object at rest or constant velocity remains so unless acted upon by a resultant force.
- Second Law: ( F = ma ) where ( F ) is force, ( m ) is mass in kilograms, and ( a ) is acceleration.
- Third Law: Every action force has an equal and opposite reaction force.
Weight is the gravitational force on an object: ( W = mg ), where ( g ) is the gravitational field strength (10 N/kg on Earth).

In free fall:
- Initially, only weight acts (no air resistance).
- As speed increases, air resistance builds up, reducing downward acceleration.
- When the forces balance, terminal velocity is reached, and there is no further acceleration.

Thinking distance is the distance travelled before reacting; increases with:
- Higher speed.
- Slower reaction times due to alcohol, fatigue, or distractions.
Braking distance is the distance from when brakes are applied until stopping; increases with:
- Higher speed or mass.
- Poor road or vehicle condition (e.g., worn tires).
Stopping distance is the sum of thinking distance and braking distance.

Objects can undergo deformation (changes in size or shape) when forces are applied.
Elastic deformation allows an object to return to its original shape when the force is removed, such as stretching a spring.