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Flashcards in P2 2 Forces Deck (24)
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What can a force do?

A force can change the shape of an object or change its motion or its state of rest.


What is the unit of a force?

The Newton (N).


What happens when two forces interact?

When two forces interact, they always exert equal and opposite forces on each other.


What happens to a boxer who exerts a punch of 100 N on an opponent?

The boxer experiences a reverse force of 100N.


What is the resultant force?

The resultant force is a single force that has the same effect as all the forces acting on an object.


What does it mean when the resultant force is zero?

The object stays at rest or at constant velocity. If the resultant force of an object is not zero, the velocity of the object will change.


Forces and resultant force

When two forces act on the same line, the resultant force is their sum if they go in the same direction and their difference if they go in opposite directions.


What happens to acceleration if the resultant force increases?

Acceleration increases too.


Important equation

F = ma

Resultant force N = mass kg x acceleration m/s^2


Fill the gap

The greater the mass of an object, the ... the acceleration for a given force



Stopping distance=

Thinking distance + braking distance.


What is the thinking distance?

The distance travelled by the vehicle in the time it takes the driver to react (ie during the driver's reaction time).


What is the braking distance?

The braking distance is the distance travelled by the vehicle during the time the braking force acts.


What increases the thinking distance?

The thinking distance is increased due to


What increases the braking distance?

The braking distance is increased by
•Adverse road conditions, Eg: rain and snow
•The faster a vehicle is travelling
•Faulty car brakes
•Worn out tyres


What is the weight and mass of an object?

The weight of an object is the force of gravity on it.

The mass of an object is the amount of matter in it.


Weight equation

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

Or W = mg


What happens when an object falls in a fluid?

When an object falls in a fluid, the fluid drags on the object. The drag force increases with speed. The object then reaches a constant velocity where the weight is equal to the resistive forces. This is called terminal velocity. The resultant force is zero.


Elastic objects

An elastic object regains its original shape when the forces deforming it are removed.


How to calculate the extension of a spring

The extension of the strip of material at any stage = its length at the stage - the original length.


What happens when an elastic object is stretched?

When an elastic object is stretched, elastic potential energy is stored in the object. This is because work is done on the object by the stretching force.


What does Hooke's law state?

Hooke's law states that the extension of a spring is directly proportional to the force applied, provided its limit of proportionality is not exceeded.


Hooke's law equation

Force applied N = spring constant N/m x extension m.

Or F = k x e.


Anti skid surfaces

The surface is tougher than normal. This causes more friction between the surface and the car's tyre.