# B Will this travel faster than light

1. Jun 5, 2016

### pinochet

if i throw a ball of matter forward in space will it travel faster than light given enough time and space with nothing what so ever to stop it i.e newtons first law of motion in effect.i figured it should becuase it will have a force to give it a constant acceleration(change in velocity).my knowledge of physics is pretty limited but i've heard no matter can travel faster than light so is my understanding of newtons law wrong.

2. Jun 5, 2016

### Replusz

Its mass will constantly grow, so the force you need to accelerate it grows too. You cant do this until you get to light speed, because then youd need 'infinity' force.

3. Jun 5, 2016

### Staff: Mentor

If you just throw something forward, it will coast at a constant speed, whatever speed it had when you let go of it. That's because after you've released it there's no longer any force acting on it, and by Newton's first law that means no change in speed.

If instead you continue to apply a force to it, constantly accelerating it, you will find that it gets closer and closer to the speed of light but never quite reaches it. The same force produces a smaller acceleration as the speed of the object increases. That's not what you'd expect from Newton's second law $F=ma$, but it turns out that Newton's second law only works for objects that are moving slowly compared with the speed of light (which happens to include everything in our daily experience, which is why we still use it).

A detailed explanation of why this happens requires learning some of Einstein's theory of relativity. You'll often hear that it is because "Einstein says that mass increases with speed". That's a good enough answer for now, but you should be aware that it is not quite right and you'll have to unlearn it if you want to move beyond a superficial understanding of relativity.

4. Jun 6, 2016

### pinochet

alright so it will start coverting its energy to mass is that what you mean?

5. Jun 6, 2016

### jbriggs444

That is a bit that Nugatory referred to as "not quite right".

As the object goes faster and faster, it has increased kinetic energy. If you consider that energy as equivalent to mass ($E=mc^2$) then one would expect its mass to increase without bound as its speed approaches that of light. So a fixed force will produce a smaller and smaller acceleration and you never quite get to light speed.

The kind of mass that includes an object's kinetic energy is "relativistic mass". https://www.physicsforums.com/insights/what-is-relativistic-mass-and-why-it-is-not-used-much/

6. Jun 6, 2016

### mrspeedybob

A better way to look at it is to understand that the faster you go, the slower your clock ticks as seen by someone who is not moving. If you were to get to the speed of light, your clock would stop. This is a statement about the nature of time, not just the nature of clocks.

If you accelerate at 1 meter per second per second, that means that for each second, your speed increases by 1 m/s. Without accounting for time dilation, it should take you about 300,000,000 seconds to reach the speed of light. But now remember that your seconds are different then seconds for the guy who's is not moving. You measure your own acceleration as constant, always 1 m/s per second, but when your clock is ticking half as fast as the guy who's not moving, he sees you accelerate at 1 m/s per 2 seconds. When your clock is ticking at 1/10 speed, he sees you accelerate at 1 m/s per 10 seconds. The last second before you reach the speed of light looks to the guy on the ground like it takes forever, so he never sees you reach that speed.

7. Jun 6, 2016

### jbriggs444

This is not complete. It is qualitatively correct, but not quantitatively.

It is not just that each tick of the moving person's clock take longer as judged by an inertial observer. The incremental increase in velocity during that tick adds to the current velocity using the relativistic velocity addition formula. https://en.wikipedia.org/wiki/Velocity-addition_formula

8. Jun 7, 2016

### Kaura

As Nugatory stated simply throwing the ball will only suffice to give it an initial velocity
With no further forces acting upon the ball it will simply maintain the same initial velocity
Even if you were to apply a force to it in order to continuously accelerate it such as throwing it at a impossibly large body of mass such as a black hole and relying on the force of gravity to accelerate it you would still have to take into consideration equations dealing with special relativity at such high velocities
No matter what one does something with mass such as a ball can never reach the speed of light
Technically you could apply enough energy to the ball to get it to 299,792,457 m/s but if I am not mistaken mathematically the amount of energy required to get that same ball to 299,792,458 m/s can be demonstrated by limit x approaches infinity as y approaches 299,792,458 the speed of light

9. Jun 11, 2016

### Bob Wolf

Pure and simple.... the speed of light is an asymptotic entity. Nothing can reach it, that alone, pass it.

10. Jun 11, 2016

### Bob Wolf

Asymptotic : You can come, forever closer, to infinity, but it will never touch.

11. Dec 14, 2016

### Justozone

9 / 1

"if i throw a ball of matter forward in space will it travel faster than light given enough time and space with nothing what so ever to stop it" The only problem, there is no force to continue it's acceleration so it's speed would remain constant. But it would accelerate due to a sling shot affect from other moving gravitational forces if it does not get trapped by them.

12. Dec 14, 2016

### Replusz

But it would still NOT reach the speed of light...

13. Dec 14, 2016

### Justozone

The speed of light has a definite value. So by this logic it is not an infinite speed. Infinite speed would be a perpetual acceleration effect.

14. Dec 14, 2016

### Replusz

He didn't mean the speed of ligth is infinte. It is NOT (it is around 300 000 km/s)
He meant you can get to its 99.99999%, but not to 100%. NEVER!
hth

15. Dec 14, 2016

### Justozone

True, this would not even come close to the speed of light.

16. Dec 14, 2016

### Justozone

Through innovation we could. In the future we could be looking at light speed like the sound barrier. Before airplanes and gun powder I'm sure we would have thought that surpassing the speed sound was impossible.

17. Dec 14, 2016

### Staff: Mentor

Mentor's note:
A number of off-topic and misleading posts have been removed from this thread, and it has been closed.