Weight Drop Experiment

Background Information - Forces Acting on Falling Objects

1. Gravity - a force that pulls all objects towards the centre of the Earth. All objects fall at the same rate, if gravity is the only force acting.
2. Air resistance - a force that builds up as a falling object speeds up. The faster an object falls, the higher its air resistance becomes. Evenually air resistance equals the force of gravity and the object then falls, until it hits the ground at a constant speed, called terminal velocity. Different objects have different air resistances and different terminal velocities. A parachute, for example, increases a falling person's air resistance and reduces termimal velocity to a safe value.
3. Buoyancy - a force that lifts an object upwards by an amount equal to the weight of air displaced by the object. For many objects, the weight of the air displaced is insignificant and the effect of buoyancy is not noticed. For large, light objects such as hot air balloons, a lot of air is displaced and the force of buoyancy is greater than the force of gravity, causing the object to rise.

Tasks

1. Read the background information above. Watch the weight drop movies and study the frame by frame sequence of falling weights. Start a new Word Document. Complete the following:
   1. Do heavy and light objects drop together? Illustrate your answer with a pair of frames.
   2. Do objects fall at a constant speed? Note: the camera takes a frame every 4/100 ths of a second. Illustrate your answer by pasting multiple images of a stone onto a single frame to show its path.
   3. The image of the falling golf ball in the frame by frame sequence is round in the early frames but stretched in the later frames. Paste copies of two frames that show this. Explain why the stretching occurs. Note: the shutter of the camera stayed open for 1/100 th of a second when taking each frame.
   4. How could the experiment be improved?
      Suggest how you could:
      1. Make the objects more visible.
      2. Drop the objects at exactly the same time.
      3. Ensure that an object is not given a slight push.
      4. Keep the camera steady.
      5. Make other improvements.
2. View Dropping Weights in Airless Conditions. Answer the following:
   1. When did Apollo 15 land on the Moon?
   2. What does the surface of the Moon look like where Apollo 15 landed? Illustrate your answer with an image.
   3. Who was the Astronaut who dropped the hammer and the feather?
   4. Why did he wear a spacesuit?
   5. On Earth, hammers fall faster than feathers. Why do they fall together on the Moon?
   6. How could you show that on Earth, a feather would fall as fast as a stone, if there was no air? Illustrate you answer.

Michael Gallagher, October 2001