Acceleration decreases?

Question

So i did this experiment by rolling a marble down a ramp and it turned out that the acceleration decreases? O_O

I thought acceleration was supposed to increase as the marble goes down the ramp? x_x

Or is my data correct? Look at this
http://i164.photobucket.com/albums/u28/vodkapop/phs.png

i calculated acceleration using the formula velocity/time

Answer 1

There's an important distinction that needs to be made: acceleration is a change in velocity.

This means that the velocity is supposed to increase at the marble goes down the ramp, but the acceleration can decrease.

As an example, if you roll a ball down a steep hill it could be accelerating at 7 m/s^2, which means that its velocity is increasing at a rate of 7 m/s^2.

If the hill becomes less steep, the ball could be accelerating at only 4 m/s^2. The acceleration of the ball has decreased, but the velocity of the ball is still increasing (though at a lesser rate).

So, in your case, as long as the marble is accelerating, its velocity will be increasing as it moves down the ramp.

I hope I was able to explain that well.

Answer 2

This was originally a Galileo experiment in which he compared acceleration due to gravitation and acceleration due to Inertial motion .
A mass moving against Gravity field will experience a decreasing acceleration ;whereas if its moving with the gravity it will experience an increasing acelleration.
Inertial motion is when gravity is not affecting the motion.
In this case acceleration is a decreasing function.That means inertially, the faster you move the smaller is the acceleration.

In The ramp scenario, if the marble goes up the ramp it is a function of the power that was given to the marble to move up the ramp;When the gravity power pushing down the marble becomes equal to the inertial power the marble will stop and fall down the ramp again. The same relationship exist when you throw a ball up in the air.Assuming friction is neglible.

Answer 3

First of all, a reality check on your results fails miserably. If you are rolling a marble down a ramp, where the only forces acting on the marble are friction and gravity, there is no way that your resulting acceleration should be greater than gravity (9.8 m/s^2).

Second, I have a question about what the 'Velocity' means and how you got it. Is it the average velocity of the entire run, or is it the instantaneous velocity at the finish line? Was it directly measured or calculated from some other measurement?

I suspect there is a flaw in your data. Take another look at how you measure the time and speed of your marble, and ensure that your methods result in accurate data.

Answer 4

i saw ur table...it shows that when it rolled down the ramp,the acceleration does increase but it comes to the end,it decreases this is because of the friction.Friction decreases the speed of the marble.

Answer 5

Issac Newton figured out gravity by rolling objects down a ramp. You must be comparing the rate of fall on a ramp to the rate of free fall.

Answer 6

Your forgetting about friction. On a frictionless ramp then yes it would continue to accelerate, however that only exists on paper and in calculations as a maximum. In reality we must deal with it.

Answer 7

if friction was absent, you would have a case for perpetual motion.