1. Ch 7 Physics
Yr 7 Ch 7 Forces wiki

2. Introduction to Forces
Honda the COG - Rube-Goldberg Machine youtube video 2:00 min
This too shall pass - Music video – Rube-Goldberg Machine youtube 3:58 min

3. Refer to the description to the right to draw a surfer on a wave and label it with 4 arrows indicating the forces working on him/her. 1 2 4 3

4. Good demo Interactive on forces

5. Forces page 246
Force A push, pull or twist that can change an object’s motion – make it speed up, slow down, change direction or change shape.
Acceleration Increase in speed
Deceleration Decrease in speed
Measuring forces Spring balances can measure the stretching caused by a force and bathroom scales can measure the compression caused by a force.
Newton (N) Unit used to measure force

6. Drawing forces page 246

7. Balanced forces page 247
If the forces acting on a body are balanced, it will either remain still, or continue at its original speed until an unbalanced force acts on it.
Inertia The tendency of an object to resist any change in its motion – the greater its mass or speed, the greater its inertia/momentum.
Draw diagrams and 7.1.6

8. Balanced forces page 247

9. Unbalanced forces page 247
Whenever the forces are unbalanced, the motion will change: Draw and label both the accelerating and decelerating diagrams.
nb With this in mind – redraw your original surfer with accurate arrows.

10. Inertia page 247
Inertia is the tendency of an object to resist any change in its motion (eg a school left on your bedroom floor will stay there unless you apply an unbalanced force to pick it up, or a space ship to continue at a very high speed and course unless gravity or thrusters are applied to change its direction or speed.)
Newton’s First Law states:
An object at rest will stay at rest unless an unbalanced force makes it move
An object in motion will continue moving at the same speed in the same direction unless an unbalanced forced is applied to it.
As the mass of an object increases, so does its inertia (momentum)

11. Assessing forces – draw and complete this table
Situation
Forces –
Balanced/Unbalanced
Explanation
Parachute falling at a constant speed
Car accelerating
Team losing a tug-of-war
Car parked on a hill.
Gravity = Air resistance therefore constant speed
Balanced
Driving force of the engine is > than friction.
Unbalanced
Unbalanced
The stronger team applied > force
Balanced
Gravity = park break
When you finish, read ‘Car safety features p 249’

12. Page 252

16. Friction page 255 Friction Force that acts against an object’s motion
Contact Force Force that acts between two objects that touch, or are in contact; for example friction
Friction depends upon:
How rough the contact surfaces are
How hard the surfaces are pushed together
The mass of the object

17. Air resistance and drag
Air Resistance or drag Friction that acts on an object moving through the air
Lubricants Fluid, such as oil, used to reduce friction between moving parts
Lift, weight, propulsion and drag