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 Honda the COG - Rube-Goldberg Machine  This too shall pass - Music video – Rube-Goldberg Machine youtube 3:58 min This too shall pass - Music video

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 3 4

4. Good demo Interactive on forces

5. ForcesForces 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. Force  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 Newton (N)

6. Drawing forces page 246

7. Balanced forces 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 unbalance 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 momentum. Inertia  Draw diagrams 7.1.5 and 7.1.6

8. Balanced forces Balanced forces page 247

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

11. Page 252

15.  Friction Force that acts against an objects motion  Contact Force Force that acts between two objects that touch, or are in contact; for example friction  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