P10 Forces and Motion

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Newton's 2nd Law of Motion

An object's acceleration is directly proportional to its resultant force and inversely proportional to its mass. Velocity increases if the resultant force is in its direction, but if the resultant force is in the opposite direction of velocity, it decreases.

Force (N) = mass (kg) x acceleration (ms^-2)

Acceleration (required practical)

Use the Newton meter to pull the trolley along at constant force within a given distance. The acceleration will increase if force increases, but will decrease if mass increases. Double or treble the total moving mass by using double-decked or treble-decked trolleys. For safety, protect yourself from falling trolleys.

Inertia

Inertia is the tendency to stay at rest or in uniform motion, a measure of how difficult it is to change the velocity.

Inertial mass = force/acceleration

Weight

Weight is caused by the gravitational attraction between you and the Earth, and mass depends on the quantity of matter. Gravitational field strength on Earth is 9.8N/kg - this value won't be given in the exam.

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

Terminal velocity

An object's acceleration increases as it falls down, because friction increases as it speeds up. The acceleration and resultant force then decrease. Then a constant velocity where friction will become equal and opposite to the object's weight will be reached, and there will be no acceleration - terminal velocity.

Braking force

Braking force is needed to stop a vehicle, and it depends on the speed when the brakes are applied and mass. If the speed is great, the deceleration needed to stop will be greater, and if the mass is great, the braking force will be

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