Gymnast

Parts Needed:
  • 2 Models

  • PVC 30"

  • Strong string 10"

  • Clothes pin/peg. Old fashioned, with head

  • Wood, 1 x 2, maybe 3" long

  • Straws

  • Baling wire

 

Extra Tools: 
  • PVC Cutters

  • Black tape

  • Drill, platform 15/64 bit
     

Project Description:

Levers are some of the simplest and most important machines that humans use. We use them in all kinds of situations situations, from crowbars and wheelbarrows to tweezers and seesaws. All levers have three important parts: the resistance arm, the force arm, and the fulcrum. These three parts can be arranged in any position relative to each other - the resistance arm and the force arm can even be the same part of the lever. 

A fulcrum, or pivot, is a place where something is connected, and yet can still move. You can demonstrate a pivot by swinging your arm from the elbow - you arm is connected, but it can still move freely. The resistance arm of a lever is the length which is doing the action - lifting, moving, or throwing. The force arm of a lever is the length where the force is applied - the handle of the car jack. A cool thing about levers is the way they multiply force and motion - we can apply a small squeeze at the base of the PVC pipes, and this translates to a larger motion at the top of the pipes, pulling the string tight. 

Our gymnast is swung through the air by the action of two sets of levers: the long PVC pipes and the cardboard arms of the little person. The PVC levers have their resistance arm above the block of wood, their fulcrum at the block of wood, and their force arm below the block of wood, where we apply pressure to make the gymnast move. The cardboard arms have their pivot at the string closest to the body. This is where the arm spins. The force is exerted by the other string trying to move downward as it is tightened by the PVC spreading apart. The resistance is the body of the little person as it is lifted into the air. 

The third piece of this project which makes the gymnast move is the string. Since the string goes down and up to get through the holes in the hands of the little person, it is not in a straight line. When it is put under tension by the motion of the PVC pipes, it tries to return to a straight line, bringing the little person with it. This is because a straight line is the most efficient way for a material to deal with tension - the tension can be evenly distributed along all parts of the line; a nice demonstration that the shortest distance from point A to point B is a straight line. 

Concepts:

  1. A simple machine is something that helps us do work.

  2. A lever is one of the simplest machines. There are three levers in this project: the arms of the gymnast and the two pipes.

  3. A lever has three parts: the place where the force goes in, the place where the force comes out and the fulcrum, or pivot point.

  4. A bit of force at the two holes in the gymnast's hands makes the arms push the whole body around. Likewise, a bit of force inward at the bottom of the pipes pulls the strings outward at the top. 

A Bit More Info:

The gymnast shows various phenomena of mechanics and simple mechanics. First, pulls the two strings tight and they move toward the position of least distance. This gives a twisting motion to the hands of the gymnast. This is an example of linear motion being converted to rotational motion.

Second, the push that the strings give to the hands is fairly strong, but over a short distance. The arms multiply that force so that the shoulders of the gymnast move a much larger distance. The body connected to the shoulders then moves is response to them. If you put the hand holes farther apart, this would increase the force turning the hands.

The sticks in this project are also levers. The pivot point of a lever, called the fulcrum, is where it doesn't move. In this example, the pivot point is near the middle at the 1x2 cross piece. When you push the lower ends of the sticks together, the upper ends are pulled apart. If the fulcrum is exactly in the center, the force you put in will be exactly the same as the force given to the strings. If the fulcrum is more toward your hands, the force on the strings will decrease; more toward the gymnast and the force increases.

This little gymnast has trouble standing on its hands at the top because it doesn't have any muscles, nor any nerves to control its body. Real gymnasts have to be strong and use their brain and muscles to stay balanced at the top of a pole. 

Other places we see levers are on jacks, scissors, ice tongs, staplers, brooms, scales and wrenches. 

 

Questions:

  1. Real gymnasts can stand on their hands at the top of a pole. Why can they but this gymnast can't?

  2. What are other places we use levers in daily life?

  3. What would happen if you made the gymnast twice as big?

  4. What would happen if you put the holes in the hands farther apart?

© 2020 by Victoria Matelli, Calvin Norwood, Jade Murray

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