Vehicle forces

1
Vehicle forces

• Aerodynamic drag, rolling resistance, motor
  torque, gravity, normal force

2
Car in windtunnel
3
Car in windtunnel
4
Review forces

• Gravity pulls you down
• Normal force pushes you back up
• Wind pushes car backwards
• Rolling resistance opposes wind
• Aerodynamic drag opposes wind

5
quiz

• Which has the least drag?
• Sports car or a mini-van?
• convertible or a mini-van?
• Sports car or convertible?
• Which is easiest to push?
• Baby stroller or wagon filled with bricks?
• Sports car or a mini-van?

6
Time for lab

• Working in groups of 3 or 4, you will be testing
  rolling resistance and aerodynamics
• Place matchbox cars, one at a time, on cardboard
  with one end raised a ¼ inch.
• Measure how long it tkes each car to toll down
  the incline. When you have 6 cars with times
  within 1 second of each other, move on to
  windtunnel design.

7
Windtunnel
8
Windtunnel design

• Settling Chamber - straighten the airflow.
• Contraction Cone - takes a large volume of
  low-velocity air and reduces it to a small volume
  of high-velocity air
• Test Section - where the test articles are
  placed.
• Diffuser - slows the speed of airflow
• Drive Section - provides the force that causes
  the air to move through the wind tunnel.