Can someone please explain how mass changes when travelling at very high speeds?

This is tricky. As Grintable notes, it is not the mass that changes, it is the relativistic momentum. One could say that the mass 'appears' to change, but it is important to grasp that this is really a question of appearance, not objective reality.

It gets complicated. If you were travelling in a spaceship at near to light-speed, you would not notice any change in your mass or momentum at all. You would notice that the 'apparent' mass of objects on Earth would have increased, since relative to you, they are moving at near to light-speed. And they would see the same of you. (I like the analogy of you seeing me get smaller when I walk away from you, and I seeing you get smaller.)

It gets clearer that this is an observed change and not an absolute change, when you consider that a third observer, travelling, say, closer to the speed of light relative to the Earth would observe that the momentum and apparent mass of objects on both the spaceship and Earth were different again from the observations of the people on each of these.

If you are new to this, and, um, your head does not hurt to think about it, you have probably not understood it correctly.

The rest mass m does not change. What changes is the inertia of that rest mass so that it behaves like a much bigger mass M > m.

Rest mass is the mass of an object when it's relatively still so that its velocity is v = 0. Rest mass is the one we see in e = mc^2 which is the mass-energy equivalency equation from Einstein's special theory of relativity.

The equation for the increased inertia is M = m/sqrt(1 - (v/c)^2) where v is the speed of the platform with rest mass m and c is light speed. L(v/c) = sqrt(1 - (v/c)^2) is the Lorenz transformation, which is just a math term to convert rest mass m into the inertial mass M. There are no forces in this transformation.

There is also no mass contraction. The rest mass remains at m throughout.

However, there is a length contraction that goes like L L(v/c) = l; where l is the length of the platform as seen by an outside observer. L is the rest length of that same platform when v = 0. Length in this case means in the direction of travel.

Not to confuse you even more, but to complete the mass, length, time trilogy, there is also a time contraction T L(v/c) = t; where T is the rate of time on your Rolex and t is the rate of time on the Timex of a crew member on board the platform going v velocity relative to you. This effect is called time dilation (stretching).

PS: I'm with Randy, will the person who gave gintable the thumbs down step forward and tell us why you find fault with the card table's answer? Perhaps you could enlighten the rest of us.

gintable is correct (and so of course got a thumbs down).

The only sense in which mass "increases" is that the expression for momentum becomes gamma*m*v instead of m*v, where gamma is the relativistic factor 1/sqrt(1 - v^2/c^2). This is a number that is equal to 1 or only very slightly more than 1 at ordinary speeds, but grows without limit the closer and closer you get to c. Accelerators operate with gamma factors in the thousands or even millions.

Anyway, originally this increase in momentum or inertia was described by saying m*v is replaced by m_rel*v, where m_rel is the "relativistic mass". But all you're doing is defining relativistic mass as gamma times the actual mass. The mass doesn't increase in any real sense. You don't have more particles. You don't exert more gravitational force.

For this reason many people these days have dropped the term and consider m to be a constant, and write the gamma explicitly.

If speed not change the mass the same.And even changing too.On Mars for instance something.And so frequency of tools.Attention! It mean that if you want radio,or be on bord such ship need some change frequency and volume of ships mass.It hard for changing speed it acceleration and mass no mass at all.It find out from differential equation of classic formulas for moving and impulse.

in basic terms. As a physique speeds up it desires extra potential to maintain the acceleration going. So, a motor vehicle going from 0 to twenty desires much less potential then going from 20 to 40. it is via a upward push in mass. The extra suitable the fee, the extra potential required to strengthen up. because of the fact the fee methods the fee of sunshine, mass methods the countless. So, the potential required to strengthen up methods the countless. this implies each and all the potential in the universe can not strengthen up a physique to the fee of sunshine. This, of direction, purely applies to a large physique (i.e. a physique that has an inherent mass).

Well, it isn't really mass, as in amount of material in an object, that is changing.

But rather it is inertia, as in the 'm' in Newton's second law of Fnet = m*dv/dt.

it will be harder to change its speed