why does velocity change?

Answer 1

Because outside forces act on whatever it is that's moving (gravity, friction, air resistance, etc.)

Answer 2

One of Newton's laws of motion says an object will stay at a constant velocity or at rest (v = 0) if and only if there is no net force (f) acting on it. This is often referred to as the Law of Inertia or, alternatively, the Momentum Law; where momentum = p = mv; and m is the mass of an object traveling at v = constant or = 0 velocity.

Now if we wanted to change velocity over time, we could write that change as dv/dt; where dv means change in velocity and dt means change in time. From p = mv, if we change velocity the equation becomes dp/dt = mdv/dt because d_/dt has to be applied to both sides of the equation to keep it balanced. It's like (d_/dt)p = dp/dt = mdv/dt = m(d_/dt)v = (d_/dt)mv = (d_/dt)p, which shows the equation is still balanced.

Now, we have dp/dt = mdv/dt = ma = f; where dv/dt = a, which is acceleration. A change in velocity is acceleration. And there we have another of Newt's laws: f = ma or f/m = a where f is a net force applied to the mass m to give that mass acceleration a = dv/dt, the change in velocity.

The last of Newt's laws of motion addresses motion when f = ma = 0, which says the net force is zero on the object. In which case, we have a = 0 = dv/dt. That is, f/m = 0 and, since m > 0, we have f = 0. Which means, from the first law v = constant or zero since there is no net force to change the velocity.

When f = 0, that means the sum of all forces acting on the object is zero. The only way that can happen in general is to have an equal but opposite force for all forces on that object.

Answer 3

the acceleration of an object is directly proportional to the net force acting upon the object and inversely proportional to the mass of the object. When combined with the definition of acceleration (a=change in velocity/time), the following equalities result.

Answer 4

outside forces or the object itself. If it changes directions, that is considered a change of velocity.

Answer 5

Velocity of a moving Mass is oscilliatory. The reason is that during the dispacement of Space as the Mass moves ,it encounter different space densities as space gets compressed during the displacement.
Velocity square is directly proportional to the pressure of space upon the mass and inversely proportional to the density of the mass as it incrementally displaces Space.

Answer 6

Velocity only changes if an object is accelerating

Answer 7

Only by the action of an outside force

Answer 8

The moving object is accelerated or slowed down by external forces applied to it.

Answer 9

Because of resistance.