Here at the University of Birmingham Observatory, on many nights aspiring astronomers and astrophysicists
will be looking out at the Universe.
Through a telescope like this one, we can observe many stars, planets and even moons.
In fact on our very own moon, Apollo astronaut Neil Armstrong performed a very interesting
experiment In one hand he held a hammer, and the other
a feather.
He dropped them both at the same time.
Which do you expect to hit the floor first?
Here on Earth the hammer hits the floor first, but on the moon they both fell to the ground
at the same time.
This is because on Earth the feather experiences more air resistance.
To demonstrate this, let’s try again with 2 objects of the same shape.
Here I have a light ping pong ball and a heavy metal ball.
Which do you expect to hit the ground first?
So despite the differences in weight, the balls hit the ground at the same time.
However, the time the it takes to hit the ground will be a lot longer on the moon than
on the Earth, and this is to do with a special number we call little g.
It’s a measure of the acceleration.
Let’s see if we can measure little g in the lab.
Here I have 2 light gates set up.
1 to measure the start time and the other to measure the
end time.
The distance between them is … meters.
First we need to make sure the data logger is set to zero.
Then I can drop my mass through the light gates
The data logger tells me the time it took for the mass to fall from this light gate
to this light gate.
In this case it took … seconds Let’s repeat this a few more times and take
an average And we can repeat the experiment for various
distances between the light gates.
Recall that the distance travelled is related to acceleration in the following way:
Since g is the acceleration we can replace a with g and rearrange the equation in the
following way: This means that if we plot a graph of 2 times
the distance over time against time, then little g is simply the gradient
So we got quite close, the true value of g on earth is 9.81m/s^2, whereas g on the moon
is just 1.63m/s^2, so on the Moon the hammer and the feather would have fallen much slower
than they did here.
Gravity is a big research interest here at Birmingham, with projects that include trying
to determine Newtons Universal gravitational constant (Big G) to as high accuracy as possible,
Detection and theories of radiation due to gravity (Gravitational waves), and even the
effects of gravity on light - did you know that gravity can bend light?
The distortion is called gravitational lensing and is just one way we have used to map dark
matter.