 What is a ‘lever arm’?

 Distance from the axis of rotation to where a force is applied

 When the net torque on an object is equal to ZERO  Balanced objects (not rotating) are in rotational equilibrium

 Why will a non rotating bike wheel topple while a spinning wheel will stay upright?

 Conservation of Angular Momentum, the direction of the angular momentum cannot change without an outside torque being applied.

 How might you kick a football so that it leaves the foot with no rotation?

 Kick it (apply a force) directly to the COG  If kicked above or below COG, then torque would be applied and rotation would occur

 How would you move the circle so that the rod was more balanced?

 Move circle closer to the axis, thereby giving it a lower lever arm… and therefore a lower torque is being produced by it

 Why when Mr. Schober flipped over the spinning wheel while sitting on the stool did he then start to rotate?

 Cons. Of angular momentum, Schober, wheel and stool are all a closed system…  By flipping the direction of the wheel we changed its “L”, so then Schober and stool rotated in opposite direction, so that the total L of the whole system stayed constant

 which direction did Schober start rotating… the original direction that the tire was rotating??, or the new direction that the tire was rotating? ?

 Original Direction

True or False?  In order to balance, the total forces on both sides of the axis of rotation need to be equal.

 FALSE  The total torque on each of the axis needs to be equal  AKA…. Total torque on left side = total torque on right side  Torque….. NOT Force

 How can a person reduce the rotational inertia of their body?

 Making their “radius” smaller by pulling their body into a tight ball that is close to whatever axis they may be rotating on

 Ice skater is spinning with arms and legs out, then pulls them in tight to their center? What happens? And Why?

 They gain a higher rotational speed, because of the law of conservation of angular momentum.

 Solid cylinder and hoop each of the same mass and radius roll down an incline…. Which will make it down the incline faster? Why?

 Solid Cylinder because it has a lower rotational inertia…. Because more of its mass is concentrated towards its center

Using right hand rule which direction is the angular momentum?

 In to the wall

 A helicopter’s blades are rotating clockwise during a flight, if the tail rotor then breaks, what way will the body of the helicopter rotate?

Counterclockwise

Using the right hand rule, what would be the direction of the angular momentum of the below cylinder.

 Up I

 When trying to walk a balance beam why do you hold your arms out away from your sides?

 To increase rotational inertia by moving part of your mass further away from the axis…. In other words… increasing your average radius

1 kg ??

True or False  RPM is a unit for rotational speed

True

In what direction is the centripetal force always pointed?

Inward, toward the center of the circular path

On the below rotating disk, which point has the highest linear speed? Rotational speed?

 A) Star, covering the largest distance in the same amount of time  B) All points have the same rotational speed

 A 1000 Kg car and a 1500 kg car travel both travel at 15 m/s around a circular track. For which car will it be harder to stay in a circular path? (in other words… which car will require more centripetal force to keep it on a circular path)

1500 kg car  Has more mass, so has more inertia and is harder to keep in a circular path

 Two 1000 kg cars are travelling on a circular track, one at 15 m/s and the other at 20 m/s, which one will require more centripetal force to keep it on its circular path?

 20 m/s car, has largest tangential (linear) speed. Harder to keep object at a high speed in circular motion

 Is Centripetal Force a quantity that is more relevant for something that is rotating or revolving?

Revolving

What is centrifugal force?

 “Fake” force that gives the illusion of an outward force during circular motion  Is actually just an object inertia

Where does an object’s CoG have to be in order for it to balance?

Directly above its support base

When left to rotate freely, an object must rotate about an axis that goes through its _________.

Center of Gravity

Why is a lot of frozen ice on the deck of a big boat bad for the boat?

It raised the CoG and therefore makes it more likely to topple it is hit by a big wave