Physics Demonstration: Projectile Motion

Uploaded by cafedurhamcollege on 10.08.2012

Hi! I’m Dave Schuett from Durham College and
in this physics video we’re going to take a look at projectile motion.
Now a projectile is an object that travels with its path shaped only by gravity.
It might have some initial velocity, but once it’s free of the launcher it’s only gravity
that shapes it’s path. Ok.
For our projectile motion experiments, we are going to be using the projectile launcher.
Simply spring loaded launcher. So we just take our projectile.
(Noice) Push it against the spring with the plunger
and it’s set up to launch. Now to measure the speed we’re going to
use again our photoelectric gates. So as soon as the projectile moves through
it we get an indication. So we mount that and we’re ready to go.
Now we’re going to be measuring velocity, so all I have to do catch it after it’s
launched. So as it passes through the gate (noice) we
can record velocity, and from velocity we can use this equation to calculate how high
the projectile rises. Our first measurement is going to be in a
vertical shot of projectile and we going to measure the time between the photoelectric
gates. So we’ll start the timer.
Fire the projectile. (Noice)
And there’s our first set of data. So we’ve got a time of .024 seconds.
Now, we’ll do this again in order to get an average.
So a second shot. (Noice)
And there’s again the vertical shot and we’ll stop that.
And we can see very similar times in both cases.
We’ll take one more and we’ll be able to take an average.
So again we’ll start, fire the projectile. (Noice)
And that’s three vertical shots. Ok.
So our data. We’re going to take the data, may expand
this a little bit, and we’ve got three shots timed between the gate and we’ll do some
calculations. Ok.
Time between the gates and then we’ll calculate the velocity.
Now the formula used for velocity. The photoelectric gates are 10 centimetres apart for .1 metres
apart. So distance divided by time will give us the
velocity. So the first time is .024154 seconds, the
second .024156, and the third one, just behind here, .024152.
So we can see the times are very close and we can see that they all agree with an average
velocity of about 4.14. A slight variation, the average of the three,
4.14 metres per second. So that’s the philosophy we can use for
the vertical shot. Ok.
Now that we’ve done a vertical shot, we’re going now go from the vertical to the horizontal.
So we adjust the launcher so that now we’re going to launch at zero degrees horizontally
and get our true projectile motion. (Noice)
OK. We’re now collecting the data on the horizontal
shot. I’ve already done two shots and I’ve collected two pieces of data.
So let’s do the last one. I’ve loaded up the projectile launcher.
It’s set to horizontal. So we’ll start the timer and fire the projectile
launcher. (Noice)
And there’s our last bit of data. So again we’ll put into our spreadsheet.
I’ve already got the first two entered. The last one we have 0.023558 and with that
we get an average velocity of 4.22, so that’s the average velocity for our horizontal shot.
Ok. For our next launch, we’re doing a vertical
launch. And we’re also going to test during this
launch or confirm the idea that the projectile that’s launched will take the same amount
of time to hit the desk as a projectile that’s dropped from the same height at the same time.
Now to do that, we’re going to be using this drop box.
Now this drop box will be set to drop the projectile, drop this ball bearing at the
instant the other is launched. To do that, we’ll just take our sensor from
the very first gate and we’ll plug it into the drop box controller.
So now we’re set that as soon as the projectile launches, this ball bearing will drop.
(Noice) Ok.
Now that we’ve done the two shots, vertical and horizontal, we’re now going to have
true projectile motion by shooting at an angle. So we’re going to adjust the launcher to
a 30 degree angle and this way we’ll give the projectile both vertical and horizontal
velocity. (Noice)
We’re now at 30 degrees for our projectile launcher. Again I’ve taken two measurements
and I’ll take the third. So we’ll start the data collection and fire
the launcher at 30 degrees. (Noice)
And there’s our third set of data. Ok.
So adding it again to our spreadsheet, just like we did before.
I’ve got the first two already added. The last one .023956 and that gives us for our 30 degree shot an average
of 4.17 metres per second. Ok.
There you have it! We now see that we have projectile motion
and we did three experiments, vertical, horizontal, and a combination at an angle.
For more information you will be able to see the equation worked out in our math section.