Work Power and Energy But we will start

Work, Power and Energy But we will start with torque. . .

Torque T=Fr(sinΘ) T is torque in Newton meters or Joules r is radius in meters (may also be a d for distance) F if force in Newtons Torque is the force applied to a rotating object (wheel) perpendicular to the radius and parallel to the edge of the object.

Other examples of torque. . . Turning a door knob Opening a “hinged” door Moving through a revolving door Opening a jar Operating a jack to change a tire Lifting something with a simple lever (crowbar)

Torque also depends on the angle between the force and lever arm. For example, a “doggie” door hangs straight down and as the dog goes through, the angle of F changes. (see why I'm not an art teacher) T=Fr(sin θ)

Example 1: Calculate the torque applied by a 3. 0 N over a 15 degree turn to a door knob with a radius of 3. 1 cm.

Example 2: Calculate the net torque applied to a basketball tipped by 2 players at the beginning of a game. Player A tips with 15 N at 0. 14 m while player B tips with 11 N at 0. 7 m from the opposite sides of the ball.

Power

Power is work completed over a period of time. P=W/Δt P=Fv P=mgd/t

Example 1: A 193 kg curtain needs to be raised 7. 5 m in 5 seconds. There are two stage motors available. Motor 1 has a 5. 5 kilowatt capacity and motor 2 has a 3. 5 kilowatt capacity. Which motor would be best for this job?

Machines A machine is a device used to multiple the force or change direction of an applied force. Some simple machines include a lever, a pulley, a wheel and axel…

Remember that work is equal to force applied over a distance. If work is conserved (like energy, mass, matter), then: Pin = Pout

Example 2: A woman pushes a lever down with a 10 N force. The lever moves 1. 0 meters. At the other end of the lever is a 50 lb boulder. How high will the boulder be raised?

Example 3: The escalator at the mall is broke so you will have to walk up the stairs. If you weigh 150 lbs and the to walk up a vertical distance of 25 m, how much work must you do? If it takes you 15 seconds to walk up the escalator, how much power would you expend?

Homework: Page 181 #1, 3, 4 and Section Review #1