Physics Demonstration: Acceleration of a Free-Falling Body

Uploaded by cafedurhamcollege on 10.08.2012

Hi! Today we are you going to take a look at “gravity”. Now we know the gravity affects
us whenever we're near a planet, but what we're going to take a look at today is
exactly how does it affect us.
Does it give us a constant velocity towards the planet? Does it give us a
constant acceleration? How does it affect our position in space? We are going to take a
look at that with a simple desk top experiment.
Okay. So this is where we're going to take a look at measuring acceleration
new to gravity.
We've got an experimental setup
right here. What we are going using is a photoelectric gate.
So when this gate, whenever something passes between these elements,
it indicates electronically that something's passed through.
So will be able to use that
to look at a falling object.
What we are going to take a look at falling is something called the “picket fence”. Just a
piece of uh... plastic with the black bars on it
so as it falls through we’ll be able to
calculate the velocity and acceleration.
From that gate we hook
to a digital adapter that converts pulses into binary.
That connects to a USB adapter
so that we can record it on the laptop.
And we will be able to record in a chart format.
This is the display area in the data studio’s
graphing program.
It's going to display the data that we collect from our sensors.
We've got three charts. The first one is position in metres.
The second one is velocity in metres per second.
And the third one is acceleration in metres per second squared.
So we'll do the first drop.
So we're all set up to go and we're going to drop this through
(noice) just like that!
And we've recorded the data
and you can be able to see on the data how the position has changed, the velocity has
changed, but the acceleration
is fairly steady.
Now some things can vary our experiment a little bit.
As I drop it, if I drop it a little bit canted, then that's going to affect how it
measures the rate through.
As it drops if the air buffers and moves it around that will also affect it
slightly. So that can have some affects. So usually we use several drops in order to
be able to average the value.
Okay. So again we’re going to drop the picket fence through
and record the data as it drops.
Ok. Time to collect some data.
Scales changed up a little bit. We do a drop.
Picket fence is going down. (Noice) And there’s some data.
So let’s take a look at this data.
At the very top we've got position. So we see the position constantly changing
and probably if we zoomed in a little bit of a slope to that,
little bit of a curve.
Now in the velocity in the second graph we've got a fairly straight line, a linear line,
that shows that velocity is increasing at a steady rate.
So if we have a change in velocity it means we do have an acceleration and we see
that in the bottom graph.
We've got a fairly constant acceleration.
If I zoom in on that, pull it down a little bit, and then expand the scale,
and let me just do that again, 0:03:09.559,0:03:13.949 as we expand the scale we start to see a good set of data.
We've got,
let me expand a little bit more,
about 9, just between 9.5 and 10.
And taking a close look we’ve got 9.5, 9.6, so almost
9.7, there’s a 9.7 up close to a 9.8,
9.7, 9.8. So we’ve got a good collection of data there.
Now again there's a little bit of variance and we’ll see that as we take
different sets of data. We will find some variation. Uh...depending on the drop
and everything else. So that's a good set of data. Okay. So now we're going to attach
a weight the picket fence,
and test whether or not mass has an affect on the acceleration due to gravity. (Noice)
Okay. Now we're going to drop the picket fence with a weight attached to it.
So I’ve already attached the weight.
Now let’s see what kind of data we’ll get.
And there's our data. Only 3 points. It was a little bit difficult to get it
set up with the weight attached, but I think that's still a good measurement.
We take uh... a close look in,
and we can see that our data still
just below 10 on the average.
So again around this point
uh... just below 10
and that's a good data set for the weight. A little bit cumbersome with the weight
uh...instead of taping it around with black tape we could try a few of the ways to
weight it down. But we’re going to get basically the same thing.
That the acceleration is the same with or without the weight. We just get a
little bit more variance because of the uh...
it’s a little bit awkward with the equipment.
Okay. So what you saw on the experiment
was anything falls towards the center of the earth with a constant acceleration.
Even with the different mass it doesn't matter.
We can think of gravity as an acceleration field. Everything within that field
accelerates at the same rate, as long as we take into account things like air