4.3 Work part 1

• Natuurkunde
• Middelbare school
• vwo
• Leerjaar 3

Planning

• Recap:  Resultant forces and graphs
• New:  Work

This graph depicts a(n)

1. acceleration
2. uniform motion
3. deceleration
4. standing still

This graph depicts a(n)

1. acceleration
2. uniform motion
3. deceleration
4. standing still

This graph depicts a(n)

1. acceleration
2. uniform motion
3. deceleration
4. standing still

This graph depicts a(n)

1. acceleration
2. uniform motion
3. deceleration
4. standing still

Fres<0

Fres>0

Fres=0

Work

Work = Force x distance

W = F x s

• Without force there is no work
• Without movement there is no work
• If the force works perpendicular to the movement that does not provide work

In which of these examples there is work being applied?

1. Arm wrestling between two people of equal strength
2. Pushing against the wall of your house
3. standing still
4. Standing on an escalator which goes upwards

Calculating Work

W = F•s

W (Work)  [J] or [Nm]

F (Force ) [N]

s (space/distance) [m]

Forces of friction

During the last couple of weeks the creeks froze over so you decided to go ice skating again. The friction from the ice on your skates was very little, only 30N. You got up to a high speed and without any additional movements you glided on until you came to a standstill after a respectable distance of 70 meters.

What was the work which the ice acted upon you?

What was the work that was acted upon you?
F = 30 N
s = 70 m

Work

• Will affect the speed something is travelling in

• a negative amount of work will affect something in the opposite direction in which it is travelling (higher friction then driving forces for instance)