**Forces**

L.O

Balanced and unbalanced 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

https://www.youtube.com/results?search_query=cats+new+york+falling+news

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.