# Physics - Forces and Motion

This set is for IGCSE Physics and is on Froces and Motion. For this I have used the Stephen Pople book as guidance. This topic has six sub-topics:

Speed, Velocity and Acceleration          Motion          Gravity          Force in Balance          Force, Mass, Acceleration          Moving in Circles

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## Speed, Velocity and Acceleration

Speed can be calculated by:

speed (m/s) = distance (m) / time (s) (s = d / t

Velocity is a vector meaning it is the speed of an object and its direction. To make it a vector you add a + or - before depending on the context.

Acceleration is the change of velocity and can be calculated by:

average acceleration (m/s²) = chenge in velocity (m/s) / time (s) (a = v-u / t)

Acceleration is also a vector.

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## Motion

DISTANCE - TIME GRAPHS:

A positive gradient means the car is travelling forwards.          A gradient of 0 means the car has stopped.          A negative gradient means the car is travelling backwards.

The steeper the gradient the faster the car is travelling.          The area below is the speed of the car.

SPEED - TIME GRAPHS:

A positive gradient means the car is accelerating.          A gradient of 0 means the car is travelling at a steady speed.          A negative gradient means the car is decelerating.

The steeper the gradient the higher the acceleration or deceleration.           The area below equals the distance.

Motion can be investigated by passing a moving trolley with a peice of tape behind it which moves through a ticker-tape timer. This punches carbon dots on the tape at regular intervals. The closer the dots are the slower the trolley was moving.

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## Gravity

Gravity is another way of saying the acceleration of freefall, which is the rate of an object falling through a vacuum.

Gravity is also essential for relating weight and mass.

It relates them by using the following equation:

Weight = gravity x mass

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## Forces in Balance

A force (Newtons [N]) is a push, pull or twist that changes the shape, temperature, direction and / or speed of an object.

Common forces are: Upthrust          Weight          Tension          Friction          Thrust          Air Resistance          Water Resistance

Newtons first law is: If no external is acting on an object, it will 1. If stationary, remain stationary 2. if moving, keep moving at a steady speed in a straight line.

TERMINAL VELOCITY is when someone remains at a constant speed as two constant forces have cancelled eachother out, like a skydiver with weight and air resistance.

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## Force, Mass and Acceleration

All objects resist change in velocity and the greater the mass of an object, the greater the resistence, this resistance is called inertia.

The overall force of an object is called the RESULTANT FORCE. This is calculated by finding the difference of two opposite forces.

Force, mass and acceleration can be linked using this equation:

Resultant force (N) = mass (kg) x acceleration (m/s²) or F = m a

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## Moving in Circles

The force of an object moving another object round in circles is called the centripetal force.

The force needed to move the object in a circle is increased id the mass / speed of the moved object is increased, or if the radius of the circle is reduced.

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