P2.2

measured in newtons (N)

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

friction is a resistive force which slows things down and tries to stop objects sliding past each other.FRICTION ACTS IN THE OPPOSITE DIRECTION.

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

when the resultant force on an object is zero the object is stationary, or continues to move at the same speed and same direction if it was already moving

constant velocity= resultant force zero

When the resultant force isnt zero, the movement of the object depends on the size and  direction of the resultant force SO the greater the resultant force, the quicker the take off is for a plane. 

resultant force= mass x acceleration

acceleration= force/ mass 

mass= force/ acceleration 

If the velocity of an object changes, it must be acted on by a resultant force. its acceleration is always in the same direction as the resultant force.

The velocity of an object increases if the resultant force is in the same direction as the velocity.

The velocity of an object decreases if the resultant force is in the opposite direction as the velocity

For any car travelling at constant velocity, the resultant force on it is zero because the motive force of its engine is balanced bu the resistive forces. A driver uses the accelerator pedal to vary the motive force of the engine.

The breaking force needed to stop a vehicle depends on the mass of the vehicle when the breaks are first applied.  and the mass of the vehicle.

Thinking distance= distance travelled by the vehicle in the time it rakes the driver to react.

Breaking distance is the distance traveled by the vehicle during the time the breaking force acts.

the stopping distance= the thinking distance + the breaking distance

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

The mass of an object is the quantity if matter in it 

If we know the mass of an object, we can calculate the force of gravity on it.Weight= mass x gravitational strength.

if the objects fall freely, no other  forces act upon it. It accerlates at a speed of 10m/s2 called the acceleration due to gravity.  its acceleration is force/mass. SO 10N/1kg= 10m/s2

If the object falls in a fluid, the fluid drags the object . the drag object increases with speed.The acceleration of the object decreases as it falls.This is because the drag force increases as it speeds up so the resultant force on it decreases. 

The object will reach a constant velocity when the drag force on it is equal and opposite to its weight. This is called terminal velocity.  The resultant force is zero, therefore the acceleration will be zero.

forces between objects

resultant force

force and acceleration

on the road

falling objects