The Leaning Tower of Pisa - Galileo's Experiment

I went on holiday to Italy not long ago and whilst I was there, I visited the Leaning Tower of Pisa. This is the place of Galileo’s experiment where he dropped two cannonballs of different masses to see  whether they would hit the ground at the same time. They did. 

Many people would argue that they wouldn’t (if they didn’t know the outcome of the experiment already). This is understandable as common sense tells you that heavier objects have a larger force of attraction and will therefore accelerate towards the Earth faster than lighter ones. However, acceleration is not just derived from force, it also depends on mass (a = F/m, acceleration = force / mass, Newton’s Second Law of Motion). 

Let’s substitute some figures into a = F/m. Take a 1kg chinchilla and 100kg panda. If we were to only think about the force acting on these animals (ignoring air resistance), the panda would hit the ground first. This is because 100kg, the panda’s mass, results in 1000N of downward force (due to the Earth’s gravitational field strength of around 10N/kg). The chinchilla’s downward force would only be 10N. Now let’s put the effect of the animals’ masses into a = F/m.

acceleration = (1000 N / 100 kg) = 10 m/s/s

acceleration = (10 N / 1 kg) = 10 m/s/s

The acceleration is the same regardless of the force. The panda's mass gives it more inertia (this is an object's resistance to changes in its current state of motion), this means it is more difficult to get the panda moving compared to the chinchilla. The panda's mass has an inverse effect on its acceleration and therefore causes the two animals to accelerate at the same rate.

The Physics of Flight

I recently went on holiday to Italy, this required me to fly which got me wondering: How does an aeroplane fly whilst carrying so much weight? I went on a little journey of discovery and found out.

Takeoff

During takeoff, the plane's engines produce a great deal of force (thrust) pointing in the opposite direction of the plane's travel. According to Newton's third law of motion, this makes the plane move forwards (every action has an equal and opposite reaction). Due the movement forward, air is rushing over the plane's wings. The carefully designed shape of the wings forces this air downwards which causes an upward force called lift. This lift is what causes the plane to go upwards and the thrust from the engines is what causes it to move forwards.

Flight

The plane is now suspended in the air. It doesn't fall to ground because the lift produced by the air rushing downwards exactly balances the weight acting downwards. The plane keeps moving forwards because the thrust from the engines is greater than the air resistance.

There you have it, flight in its simplest terms.