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# Forces

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by

## Paul Sheffield

on 5 February 2018

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#### Transcript of Forces

Forces
L.O
Balanced and unbalanced forces

Starter
At which point is the skydiver traveling fastest?
At which point are the accelerating the most?
At which point are they decelerating the most?
Why do they decelerate?
HigherThinking
Use your ideas about terminal velocity to explain why a hampter could survive a fall from a 747
complete the forces on the diagrams
would they be accelerating or decelerating
Newtons First Law
100N
100N
100N
N
60N
100N
+ 30N
N
100N
-70N
N
N
Investigating resultant forces
How does force affect acceleration?
How does mass affect acceleration?
Newton’s First Law:
If the resultant force acting on an object is zero and:
• the object is stationary, the object remains stationary
• the object is moving, the object continues to move at the same speed
and in the same direction. So the object continues to move at the
same velocity.
So, when a vehicle travels at a steady speed the resistive forces balance
the driving force.
So, the velocity (speed and/or direction) of an object will only change if a
resultant force is acting on the object.
Students should be able to apply Newton’s First Law to explain the
motion of objects moving with a uniform velocity and objects where the
speed and/or direction changes.
(HT only) The tendency of objects to continue in their state of rest or of
uniform motion is called inertia.
Newton’s Second Law:
The acceleration of an object is proportional to the resultant force
acting on the object, and inversely proportional to the mass of the
object.
As an equation:
MS 3a
Students should
recognise and be able
to use the symbol for
proportionality, ∝
resultant force  = mass × acceleration
F = m a
force, F, in newtons, N
mass, m, in kilograms, kg
acceleration, a, in metres per second squared, m/s2

(HT only) Students should be able to explain that:
• inertial mass is a measure of how difficult it is to change the velocity
of an object
• inertial mass is defined as the ratio of force over acceleration.
Full transcript