Consider this question:

A ball thrown directly upwards into the air takes 10 seconds to return to the thrower. Calculate the projection speed and it's return speed.

Now some people consider both the projection speed and the return speed to be the same. But if the words "ball thrown" and "thrower" is replaced with the words "gun shot" and "shooter", it could change everything, right?

So does the upwards force=downwards force?

Imagine that you have an infinite amount of dominos(same mass) lined up(at the same distance).

And let's say that the first domino have been pushed with great force(like that of a bullet.)

Now here's the question. What will happen to the toppling speed after a very, very long time?

1. They will still topple with the same speed like the first one.

2. The dominos will slow down until it reaches a constant speed.

3. It would stop toppling at some point.

4. Other answer(please state).

Why do rugs placed on carpets appear to move of their own volition? How can a bunch of inert fibres exert the force needed to move my rug 15 centimetres in just two weeks when there is a substantial armchair on it?

I heard the question 'what happens when an Unstoppable force hits an immoveable object?' and I thought that the force would just go through the object, is this possible?

What is it in a fountain that allows the water to come surging back up through the tube? What technical device (or natural device) enables the water to be forced upwards and how does it work?

i have this Physics question from my teacher that says:

'Dogs are pulling a sled on the snow. If the dogs have stopped pulling draw the force diagram'

Well apparently the question only had three forces - gravity (pulling down), reaction forces (arrow going up), and friction (pulling the opposite directiong of the sled).

Well we also learnt that forces come in pairs so can someone please explain how this is possible. And if it is not can you please give the correct answer as I also put the force inertia which is currently wrong...

Welcome to this Friday's round-up of the week's top questions.

Ever been puzzled how you can blow both cold and hot air out of your mouth? purple2410 asked The Last Word, and got some very interesting replies.

A discussion on whether a body will use more calories and water if there is more available to it branched into the effect of weight on the speed of freewheeling downhill on a bicycle.

Here's one that has always puzzled me: how do fish get up to the top of a mountain?

Last Worder Milon has some ducks that are behaving strangely… they seem to want to play with their own version of a rubber duck. Can you explain why?

Finally, today's question gets to the lungs of the matter: what causes the burning feeling you get in your throat and lungs when you exercise beyond your normal capacity?

All the best,

Kat

Letters and comments editor, New Scientist

Specifically would an object with said increased electromagnetic bonds etc. exhibit appearances of being colder than they actually were due to the increased energy required to excite them?

Human beings have identified four fundamental forces of nature (the strong nuclear force, the weak nuclear force, the electromagnetic force, and gravity), and it appears that these four fundamental forces enable us to account for everything we observe in the universe (including all matter – i.e. all particles and subatomic particles are understood to be stable manifestations of these four fundamental forces). It appears that all other forces observed in nature can be derived from these four fundamental forces.

If it is correct that Energy is defined not by what it is but by what it can do, then is it correct to assume that energy must be some measure of the fundamental forces of nature acting upon one another?

The fact that mass (such as matter) can be converted into energy (such as in a nuclear explosion) in accordance with Einstein’s equation suggests that everything we observe in the universe is simply the various stable manifestations of the four fundamental forces acting upon one another. If this is correct, then what is a force, exactly (i.e. what is a force, not what does it do)?

According to the second law of thermodynamics, the energy of a closed system always tends towards equilibrium (because an equilibrium state has a higher probability than any other) and the overall entropy always increases. Can energy (all forms including heat, potential energy, kinetic energy, chemical energy etc.) be explained and defined by the fundamental forces of nature tending towards equilibrium?