1. More misconceptions Friction and electrical resistance Catherine Low Rangi Ruru Girls’ School

2. Four forces act on Toni and the bike while she rides: weight, support, friction and push.
On the diagram below, draw in arrows to show the directions of ALL FOUR forces acting on Toni and the bike. Label the forces.

3. SUPPORT
FRICTION
PUSH
WEIGHT /GRAVITY

4. PUSH PUSH PUSH SUPPORT SUPPORT FRICTION WEIGHT /GRAVITY FRICTION

5. FRICTION
Static
Surface friction
Kinetic
Fluid friction/Drag

6. Common phrase:
FRICTION OPPOSES MOTION
More correct:
(surface) FRICTION OPPOSES SLIDING
Drag opposes the relative motion of the object through the air

7. KINETIC FRICTION STATIC FRICTION sliding Kinetic friction
Direction object WOULD slide if there was no grip
Static friction

8. SUPPORT
STATIC FRICTION
FRICTION
DRAG
PUSH
WEIGHT /GRAVITY

9. Constant speed
Accelerating
braking

10. Rolling resistance
Support force
Direction of motion

11. Rolling resistance
Direction of motion
Overall support force

12. SUPPORT
STATIC FRICTION
DRAG
WEIGHT /GRAVITY

13. SUPPORT
STATIC FRICTION
GRIP
TRACTION
DRAG
RESISTANCE
WEIGHT /GRAVITY

14. SUPPORT
DRAG
STATIC FRICTION
WEIGHT /GRAVITY

15. Explain how the effect of the spikes on the sport shoes changes the effect of forces acting on the athlete and how this leads to an improvement in performance.
Answer: Spikes on shoes increase the effect of friction. Resulting in a greater reaction/push/thrust force.

16. ELECTRICAL RESISTANCE
R = Slope of the V vs I graph OR

17. Ohmic conductors – not an issueV I

18. The diagram below is a graph showing the voltage – current characteristics of a particular diode.
State what physical quantity is represented by the gradient of the graph line.
Answer: Resistance

19. Resistance = how hard it is to push charges through the device

20. V I V I V I

22. Halliday, Resnick, Walker

23. Serway

25. Direction you want to go
STATIC FRICTION
Direction of sliding