relation between mass and velocity

[skulldude]

This doubt arised in me just when i was holidaying with my parents in the car.

A huge load in the trunk made the car to move slow.

 

this means, mass is inversely proprotional to velocity.

 

But then i suddenly thought of einstein's theory. What he said was that ,when an object acquires the speed of light, its mass becomes infinite.

Doesn't it mean that mass is directly proportional to velocity.

 

Can anyone pls clear it to me in a liberal way as i am only a school student and cant understand complex terms...

[timo]

1) Mass is not inversely proportional to velocity. Unless you specify some constraints they are almost completely independent. What you probably had in mind is that for a fixed amount of kinetic energy mass and velocity were inversely proportional. This is not the case as E=mv²/2 => m = 2E/v², i.e. mass is inversely proportional to the square of the velocity, not velocity. Note that this example is just a guess of what you might have had in mind and not a general rule (e.g. there is no reason why a car and a truck should have the same kinetic energy).

2) Some people say that mass increases with velocity and call that definition of mass the "relativistic mass". It is not wrong to say so but in most cases it is not advisable. That's a bit off-topic, though.

3) If some value increases when another variable increases it does not necessarily have to do in a proportional fashion. Proportionality means that if one of the values is multiplied by x then so is the other. There's an arbitrary amount of other relationships that have value A which is dependent increasing as B increases without being a proportionality, e.g. A=B³.

[dirtyamerica]

Also don't forget Newton's 2nd Law where net Force=ma.

 

Your parents' car engine can only put out so much horsepower to create the force needed to move the car forward. Adding mass will reduce acceleration. If the load you guys are carrying is piles up high on the car then not only does the mass keep the car moving slow but it also reduces the net force acting on the car due to air resistance.

 

Hope ya had a great vacation!