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Running is a Drag

Drag is the force that opposes thrust on air crafts. The drag of the air makes it hard for planes to move quickly.

The shape of an object determines the amount of drag produced. Objects that are streamlined produce the least amount of drag. The more surface area you have opposing thrust, the slower you move through air.

For example, a fighter jet is more streamlined than a propeller driven Cessna.

When the students walk or run, the "wind" they feel pushing against them is actually the force of drag. Another name for drag is air resistance. A plane is aerodynamic if it has little drag or bulk.

An airplane has drag when it flies through the air. Drag makes the plane go slower. When you run, your legs have to move fast to make you run forward. The engine in airplanes makes planes go forward. This is called thrust.

If students do not feel any difference in the amount of drag between walking and running, make the analogy of wading through water – what keeps them from running faster in water? The water resistance is also a type of drag.

In this activity, students simulate the forces of drag and thrust as they run across the field in an umbrella relay.

A streamlined shape slips smoothly through the air. The closed umbrella is a streamlined shape with very little drag. However, an open umbrella is more bulky and will slow you down due to drag. An open umbrella held behind you as you run will generate considerable drag since it has no aerodynamic properties at all.

Objectives

  • Determine how manipulating the design of aircraft changes the size and direction of flight forces and link those changes to changes in the aircraft’s motion.

  • Explain how the drag force is created and what factors affect it’s size and direction.

Materials

  • playing field or gym

  • 4 umbrellas

  • 8 cones (to mark start line and turnaround point)

Key Questions

  • Part 1: Do you feel more or less air against your body when you run faster?

    Part 2: Why did holding the umbrella in front of you and behind you make a difference to your speed?How do you think aircraft decrease the amount of drag they encounter?

What To Do

Part 1

  1. Run around the playing field and feel the air pushing against your body.
  2. Run faster and notice any differences in how the air pushes against your body.

Part 2

  1. Split the class into 4 teams. Set up start and finish lines at opposite ends of the playing area.
  2. Give each team a closed umbrella.
  3. Each team lines up behind their respective starting line.
  4. On the teacher’s signal, the first student of each team runs to the finish line with their umbrellas open in front of them.
  5. On the return trip, the runners must flip their umbrellas so that they are holding the open umbrellas behind them. The students run back to their respective teams and pass the umbrellas to the next students in line.
  6. The first team to have all its players run the course wins the race.

Teacher Tip: If time permits, also try running with a closed umbrella and then an umbrella held open above person’s head. This is a simple way to show the impact of air resistance.

Extensions

  • Create a relay race with other types of drag force:
  • Friction drag: It occurs next to the surface of an object. A force created by surface roughness.
  • Form drag: A force affected by the shape of the body. Air flowing past an object breaks away from the surface to form little swirling pockets of air called eddies. These take energy from the object and slow it down. It occurs with non- streamlined objects.
  • Wave drag: A force that occurs only when planes fly faster than the speed of sound. It is caused by the interactions of shock waves over the vehicle and the pressure losses due to the shocks.