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Asked by dizzyg12 to Susan, Simon, Dilwar on 19 Nov 2013.
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Simon Langley-Evans answered on 19 Nov 2013:
Momentum is just the product of mass and velocity. A heavier object has more momentum than a light object moving at the same speed. Any moving object has momentum. If the movement of the object is to be stopped, the force applied has to be equal to the momentum. There is no change of state involved.
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Susan Skelton answered on 20 Nov 2013:
Hi dizzy,
Momentum is a property of moving objects. It is the reason your bike keeps moving when you stop pedalling and the reason you keep moving through the water when you dive into a swimming pool.To calculate momentum, you multiply the mass of an object and it’s velocity (speed): momentum=mass x velocity.
Things that aren’t moving have no momentum. Moving things have less momentum if they are light or moving slowly, and more momentum if they are heavy or moving quickly.
Momentum CAN cause a change in state of an object if the momentum changes very quickly. For example, imagine you drop a raw egg on your kitchen floor…
The egg is moving quite quickly (and has lots of momentum) when it hits the floor, but very quickly it slows to a standstill (the egg now has no momentum). Because the momentum of the egg changes very quickly, there is a big force on the egg. This is what causes the egg shell to smash and raw egg to go all over your kitchen!
Comments
Simon commented on :
Messy, but not really a state change. All of the solids in the egg are still solid, and the liquids are still liquid. Now, if the egg exploded in a massive fireball, that would be a state change from solid to gas. And we would be a lot more careful with eggs!
Susan commented on :
Yes, you’re absolutely right that it is not a physical change of state in terms of solid, liquids, and gases. I was thinking more of a change in state from unbroken state to smashed state, but I think I probably misunderstood the question! {oops!}
How cool would it be if eggs did explode though – cooking would be way more interesting! 😉
Susan commented on :
I’ve had a bit more time to think some more about this question. I think there are other (maybe better) examples of changes of state caused by momentum.
Basically, wherever there is movement there is momentum, and wherever there is momentum there is energy. Energy can cause all kinds of state changes: physical or chemical, it just depends how it is used.
A very topical example for our zone is Nitrogen triiodide (NI3) which is mentioned on the Iodine zone home page! Nitrogen triiodide is percussion sensitive, so if you touch a pile of nitrogen triiodide, it explodes!
Dizzy, I think you also asked whether momentum can cause a change in state of atoms. The short answer is yes, but the reason is a bit complicated…
To describe what happens in atoms, we have to use a complicated type of physics called ‘Quantum physics’. Quantum physics tells us that light has momentum too, and when a particle of light crashes into an atom, the light particle can be absorbed by the atom. If this happens, the atom eats the energy from the light particle so the energy of the atom increases. This means that the atom’s state changes from a low energy to a high energy (we call this ‘excited’) state.