03 Trying Hard to Pull Differently

Aim¶

To show (again) the validity of Newton’s third law.

Subjects¶

• 1H10 (Action and Reaction)

Diagram¶

Equipment¶

• Two force sensors.

• Rubber band.

• Data acquisition via Science Workshop.

• Projector to project on the monitor screen

• Trying hard to pull differently

Presentation¶

On the monitor, two graphs are presented for each force sensor. The software is set in such a way that one of the sensors presents $-F$.

Two demonstrators take each of the sensors. They start both pulling randomly. The display shows clearly that whatever they do, both force sensors measure the same force: $-F$ and $-F$ (see Figure 2).

Also, when one of the demonstrators holds his force sensor without moving it, while the other demonstrator moves again randomly, then both force sensors register an equal $F$ and $-F$. The registration does not reveal which of the two demonstrators is not moving his sensor.

Explanation¶

Again, the validity of Newton’s third law is shown.

Sources¶

• Giancoli, D.G., Physics for scientists and engineers with modern physics, pag. 82

• Mansfield, M and O’Sullivan, C., Understanding physics, pag. 119

• McComb,W.D., Dynamics and Relativity, pag. 1