This talk is aimed at GCSE/A-Level students... I wish to expand their knowledge of Weight, Mass and Gravity. Particuarly Newtowns Universal Law of Gravitation.
Why?
So..why do I want to launch a creme egg into space firstly?
Well I love creme eggs and recently had to have a rather large tooth out as result of the decay caused by the sweet lovely creme eggs. As I was sat last week watching Discovery, in alot of pain......as Discovery made it's final flight to the International Space Station, I came to the revelation, the only way I will stop eating creme eggs is if they are not everywhere, i.e. in bookshops, at tills in Boots, etc, they needed to be removed from Earth so as not to tempt me. The only way that made sense as I watched Discovery shoot into space was to launch the creme eggs into space aswell....
The first thing I need to think about is the Forces that are acting on the creme egg.....and how I can create a force big enough to overpower the force of gravity acting on the egg which is 'forcing' it toward the surface of Earth.
What is gravity?
Gravity is an attractive force between all objects that have mass. This means that two students in a class sat next to each other have an attractive force between them, this doesn't mean they 'fancy' each other it means their mass is causing a gravitational force to act between them. However, this force between two classmates is very small..but for big masses like that of the Earth. We do feel a gravitational force, and this force causes all objects on earth to accelerate toward the surface at 9.8 metres per second.
When you ask your friend their weight, if they don't take you to be very rude, they will most likely answer with a value in Kgs or stone. What they actually give you is their Mass, not their Weight.
Weight is a Force, which like all forces is equivalent to the product of Mass and acceleration.
In the case of a body of mass being acted on by the force of gravity, the gravitational acceleration (g) is equal to 9.8 metres per second...
Why is g=9.8m/s ?
Well the value of g (acceleration of gravity) we all know and love represents an speed increase of about 10 metres per second per second. But why is it 9.8/10 ? where does this value actually come from???
It actually depends on the planet!
Why? Because the planet is the large mass causing other smaller masses to accelerate toward it....It's the big mass causing the attraction.
So the value of g actually comes from equating Weight (which equals mg) to Newtown's gravitational force. This force depends on G, which is a gravitational constant , the mass of earth which is largest, the mass of the object we are trying to launch into space (or the object falling toward the earth)....divided by the distance between the centre of masses of the two masses...
In the case of the creme egg which we are trying to launch into space the distance (R), in the gravitational force equation is approximately the distance from the centre of the earth to the centre of the creme egg, which we can assume is basically the radius of the earth...
When we substitute all these values into the Newtowns force equation, firstly we notice that the mass of the creme egg cancels out, so the acceleration, g, is the same for all objects accelerating toward earth...10 metres per second squared!!!!
g only.. depends on the mass and radius of the larger mass object
What do we know about the Creme egg ?
How will we launch it?
I am assuming my arm is so strong that I can give the egg enough kinetic energy upwards to over come the force of gravity acting downwards.
Want ke bigger than potential energy, potential energy is energy creme egg would gain from being dropped from a certain height or extended radius from earth.
Think about when your at the top of the hill on your bike, takes alot less energy from your legs to get to the bottom this is cos of the potential energy you gain from working in direction of gravity. When you work against gravity going up hill have to overcome this gravitational force, which requires more kinetic energy from your legs, and will burn more calories... (calories are just a unit of energy).
To launch the creme egg into orbit we want to give it a k.e. energy larger than the potential energy it would have at the height of 'space'.
When you equate the p.e. and the k.e. you notice the m, mass of the creme egg cancels out. You can then re-arrange the equation to make v, the velocity the creme egg needs to escape the gravitational down force of earth and get into 'space'.
Subbing in the values for G, M (mass of earth) and R( radius of earth)... we first notice that the escape velocity is the same for any object, and is independent of the mass of the object, in this case the creme eggs mass....
Therefore if you can get any object to a speed of 11.2km per second.... it should get into space.
Of course, it will be alot harder to get an elephant to that speed than it will to get a creme egg to that speed :).
The speed to escape from Earth's gravity, is called the escape velocity and is 34 times the speed of sound...planes, such as a Boeing 747 travel at 560mph, therefore we need the creme egg to travel 45 times faster than a plane...
....basically, this is going to be a massive challenge.
You will realise that NASA shuttles/rockets like Discovery do not actually travel this fast...
....the escape velocity assume you give the object/creme egg this speed and it continues at this speed through atmosphere, with no loss of speed due to friction....
...... the shuttle has fuel which allows it to accelerate and increase its speed at various points, it also looses mass as it uses up this fuel, which means it does not need to travel at 11.2kms per second. They actually travel about 6,250mph.
So.....if you can give the creme egg enough energy to set it off from the surface of earth at 11.2 km per second (and it doesn't get slowed down by friction) it WILL get into space!!!
But, we are forgetting something. The shuttle is heavily shielded because it heats up going in and out of the layers of the atmosphere....the speed it goes is proportional to the heat encountured.
Shielding designers actually use the relation that the temperature is approximately 1000 times the velocity... therefore our creme egg will have to withstand a temperature of 11,200 degrees C.....
It's not looking good for our creme egg getting into orbit is it?
Questions
When I gave this talk I offered the creme egg which I was using as a prop to the best question. But no one actually wanted to eat the creme egg, (which I thought was quite rude). So of course I had to eat it........
...:)
There's probably a moral to this story some where, so if anyone has any questions or knows what the moral is please do comment below...
the moral of the story?
Anyway! I had some tough questions like , 'what is gravity?'
'what is a force?'
I am just going to let you ponder on those, as I am not convinced my answers actually helped the people asking them......
.... :S
Suggestions for the future
It has been suggested that I remove alot of the equations from this talk because they are likely to scare GCSE students...I can't remember that far back into my past, but I love equations so I am biased? Thoughts?
