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igcse physics notesprinted 23 · PDF 23
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printed 23 · PDF 23
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Forces are unbalanced if the effects of the forces acting in each plane do
not cancel out
There is a resultant force in one or more planes of direction
Calculating resultant force
Force is a vector quantity, it has both magnitude and direction
When adding forces together, it is important to assign positive and negative
values to show the direction in which the forces are acting
If forces are being applied in the the same direction (on the same plane of
action), they are added (e.g pushing an already moving cart)
If forces are being applied in the the opposite direction (on the same plane
of action), they are subtracted (e.g stopping a rolling ball)
Newton’s First law of motion
Newton’s First Law of Motion states:
“Objects will remain at rest, or move with a constant velocity unless acted
on by a resultant force”
Newton's first law means if the resultant force acting on an object is zero:
A stationary object will remain stationary
An object moving in a straight line at a constant speed will continue to
move in a straight line at a constant speed
When the resultant force is not zero, it accelerates
The speed of the object can change
The direction of the object can change
Newton’s Second law of motion
Newton's second law of motion states:
“The acceleration of an object is proportional to the resultant force acting
on it and inversely proportional to the object's mass”
A resultant force acting on an object will cause a change in the object's
motion
This change in motion is an acceleration:
Speeding up
Slowing down
Changing direction