Conceptual dynamics questions?

Question

For you to think about:

- Say you're in a space shuttle with twin babies. You want to be able to compare the heaviness of these two babies, but all you have is a spring balance. In space, the balance can't be used to measure the weight of anything because you feel as if youre weightless. How then, can you use the spring balance to compare?

- A rope has a 750N tension resistance force. You and friend pull on opposite ends, each with a force of 500N. Will the rope break? (No angle, you're pulling directly opposite from your friend) Why.

Answer 1

Apparently not much thinking has happened over the last 5 hours since you asked the question.

First, are you talking about a spring scale or a balance? The answers could be different.

Second, add three spring scales to this apparatus. One at your end to measure the force of your pull; Another at your friend's end. Another in the middle of the rope to measure the force on the rope. What would they read?

Answer 2

Conceptual indeed!!

In a "weightless" environment, "heaviness" has no meaning. To compare the masses of the twins, I would do as follows:

@}-
..... I
..... I I
..... I---I <------Apply a push here
..... I I
..... I
@}-

Whichever baby moves closer to the right, compared with the other is the more massive!

For the second part, consider what would happen if one end of the rope was tied to a wall. If you pull on the rope with a force of 500N, the wall pulls in the opposite direction with an equal but opposite force......500N. If you put a scale on the rope, it will only show 500N, not 1000N. Now, replace the wall with your friend. When you pull against eachother, each with a force of 500N, the outcome is the same. So, no, the rope will not break. When describing forces, there is always assumed to be an equal and opposite reaction force (Newton's First law...I think!). If your friend let go of the rope, your 500N force would vanish to nothing since there is nothing to pull against.

Answer 3

1) If the shuttle accelerates at 1g, you can use the spring scale just like you were on Earth.

2) Break. The pulls are in opposite directions and add.