1 / 8

Terminal Velocity

Terminal Velocity. Drag. Kinetic friction is a constant force. If there is a net force an object would accelerate forever Air resistance causes a friction called drag. At low velocity drag is proportional to velocity, F d = bv

miach
Download Presentation

Terminal Velocity

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Terminal Velocity

  2. Drag • Kinetic friction is a constant force. • If there is a net force an object would accelerate forever • Air resistance causes a friction called drag. • At low velocity drag is proportional to velocity, Fd = bv • At higher velocity drag goes as velocity squared, Fd = cv2 • The direction of drag force is opposite to the velocity.

  3. Terminal Velocity • An object may fall through the air at constant velocity. • By the law of inertia the net force is zero. • The force of drag must balance the force of gravity. • This velocity is called the terminal velocity. Fd =cv2 Fg = -mg

  4. Falling Leaves • The drag coefficient depends on the surface area. • Large surfaces – high drag • Leaves • Feathers • Papers • Small surfaces – low drag • Stones • Balls • Bullets

  5. Skydiving • Terminal velocity for a 75-kg skydiver without a parachute is about 120 mph (53. m/s). With a parachute the terminal velocity is 5.1 m/s. What are the drag coefficients? • Balance the weight and drag • mg = cv2 • c = mg / v2 Without a parachute: c = 0.25 kg / m With a parachute: c = 28. kg / m

  6. Downhill Skiing • CBS Sports has invited you to be the special science commentator for the Winter Olympics downhill ski race. • You observe the following: • The downhill course is 2.5 km long with a drop of 800 m • The coefficient of kinetic friction is 0.052 • The speed gun clocks the skier at a maximum of 130 km/h • An average skier is about 80 kg • What is the drag coefficient for a skier?

  7. Force Diagram • At constant velocity the forces must all balance. • Friction doesn’t act in the direction of the normal force. • The normal force cancels the component of gravity. Fd = -cv2 FN = mg cosq Ffr = -mkFN Fgy = -mg cosq Fg = -mg q

  8. Downhill Run • The slope of the downhill course is • sinq = 800 m / 2500 m • q = 19° • Drag force balances the force of gravity and kinetic friction. Fd = -cv2 FN = mg cosq Ffr = -mkFN Fgx = mg sinq q = 19°

More Related