Rotational Motion Chapter 8. Describing Rotational Motion 8.1.
-
Upload
mckayla-sperring -
Category
Documents
-
view
406 -
download
6
Transcript of Rotational Motion Chapter 8. Describing Rotational Motion 8.1.
Practice Problem
• What is the angular displacement in radians of a wagon that moves 135 around a circular path?
Practice Problem
• A playground merry-go-round makes two complete rotations in 9.6s. What is its angular velocity?
Practice Problem
• A car increases in speed from rad/s to rad/s in 5.0 s. What is the angular acceleration of the car?
Starting Rotation of Object
• lever arm– perpendicular distance from the axis of rotation to
the point where the force is exerted– L= rsinθ– θ=angle at which the force is applied!!!– r=distance to point where force is applied to axis
Practice Problem
• How much torque is applied if a wrench applies a force of 240N at an angle of 60.0° from the perpendicular? The wrench is 32cm long.
Practice Problem
• Ashok, whose mass is 43kg, sits 1.8m from the center of a seesaw. Steve, whose moss is 52 kg, wants to balance Ashok. How far from the center of the seesaw should Steve sit?
The Moment of Inertia
• resistance to rotation• I• kg*m2
• different for different shapes• Point Mass– I=mr2
Practice Problem
• What is the moment of inertia of a hockey puck that has a mass of 170g, a thickness of 2.5 cm, and a diameter of 7.6 cm? The formula for the moment of inertia of a cylinder is I=1/2mr2.
Newton’s Second Law of Rotation
• Replace Newton’s Second Law (F=ma) with angular terms
• a=α• F=τnet
• m=I
Practice Problem• A solid steel wheel has a mass of 15kg and a
diameter of 0.44m. It starts at rest. You want to make it rotate at 8.0 rev/s in 15s.– What torque must be applied to the wheel?– If you apply the torque by wrapping a strap
around the outside of the wheel, how much force should you exert on the strap?
– If the force on the strap were twice as great, what would be the speed of rotation of the wheel after 15s?
Center of Mass
• the point on the object that moves in the same way that a point particle would move
• Locating– Suspend the object from a point, center of mass is
along the vertical line drawn– intersection of 2 vertical lines will give a point
• Center of mass for a person– different male & female
Center of Mass and Stability
• Stable– an external force is required to tip object
• Higher center of gravity– less force needed to upset
• Equilibrium– translational equilibrium– rotational equilibrium
Practice Problem
• A 5.8kg ladder, 1.80m long, rests on two sawhorses. Sawhorse A is 0.60m from one end of the ladder, and sawhorse B is 0.15m from the other end of the ladder. What force does each sawhorse exert?– What if the mass of the ladder is 11.4kg?
Rotating Frame of Reference
• Centrifugal Force– apparent force (not real)– pulls toward the outside of the rotation
• Coriolis Effect– deflection of a moving object