Center of Gravity

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Center of Gravity

• Why can a person not touch his/her toes while
  standing with his/her back and heels to the wall?
  
• Answer 1

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Center of Gravity

• The CG has crossed the base of his/her body,
  causing him/her to topple.

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Center of Gravity

• A flat triangle has a height of 36.5cm. If the
  center of gravity for this object is 1/3 up from
  its base, at what point is the center of gravity?
  Why is it not halfway?
• Answer 2

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Center of Gravity

• 36.5/3 12.16cm, because the bottom has more
  weight so the center of gravity is more towards
  the heavier end.

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Center of Gravity

• You want to make people topple. What would you
  have to do to a persons center of gravity if
  they are lying down? Standing upright? Which
  action takes more work?
• Answer 3

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Center of Gravity

• For a person lying down you would have to raise
  its center of gravity by a large amount. If you
  want to topple a person standing up you would
  only have to raise its center of gravity by a
  little. It would take more work to raise the
  center of gravity of the person lying down.

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Center of Gravity

• Mr. Lowe is trying to balance a baseball bat on
  his finger. Where should he put his finger?
• Answer 4

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Center of Gravity

• Under the CG.

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Center of Gravity

• Where is the center of gravity of the 100 kg
  meter stick if you put  a fulcrum at the 40 cm
  mark and balance it with a 100 kg at the 10 cm 
  mark?
• Answer 5

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Center of Gravity

• right at the 70 cm mark

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Centripetal force

• A 20 kg car and a 100 kg car go around the same
  turn at the same  speed, how do the centripetal
  forces on the car differ? 
• Answer 1

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Centripetal force

• The big car has 5 times as much centripetal force

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Centripetal force

• A string one meter long is used to whirl a 0.5 kg
  mass in a circle at a constant speed of 5 m/s.
  What is the centripetal force on the string?
• Answer 2

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Centripetal force

• Fc12.5N

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Centripetal force

• A 1000kg roller coaster goes in circles at 25m/s.
  It is 25m from the center of the circle.
  Calculate the Centripetal Force.
• Answer 3

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Centripetal force

• Fc25000N

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Centripetal force

• In a spin cycle, what is the role of centripetal
  force and what does it help the washing machine
  do? Answer 4

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Centripetal force

• The walls of the washing machine exert a
  centripetal force which enables the clothes to go
  into a circular path.

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Centripetal force

• If you place a tennis ball on a flat board, move
  it in a straight line, but then have a outside
  force act upon it and make it accelerate to the
  left, where would the tennis call move? continue
  in a straight path? or change direction with the
  board? why?
• Answer 5

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Centripetal force

• there is no centripetal motion acting on the ball
  to make it go inward with the board. Only a force
  is acting on the board. The ball continues going
  in a straight path.

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Torque

• Why is the doorknob located across from the
  hinges of the door?
• Answer 1

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Torque

• It has more torque, making the door-opening
  easier.

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Torque

• A meter stick is hung from the 50 cm mark, and a
  1 kg mass is hung at the 90 cm mark.
• What mass must be hung at the 25 mark to balance
  the stick?
• Answer 2

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Torque

• 1.6 kg

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Torque

• If the lever arm is doubled, how much force is
  needed to keep the torque the same as it was with
  the not doubled lever arm? Answer 3

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Torque

• Half

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Torque

• In a challenge two people push perpendicularly on
  a beam one at each end. If the length of the
  beam is 7.00 m and each person pushes with a 190
  N force, what is the magnitude of the net torque
  applied to the beam?
• Answer 4

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Torque

• 1330 Nm

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Torque

• Mr. Lowe is trying to unscrew a tight nut with a
  wrench. The wrench is 30 cm long. He applies a
  force of 70N. How much torque does he produce?
• Answer 5

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Torque

• 21 Nm

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Moment of Inertia

• If a tires diameter is halved, does the moment of
  inertia halved? 
• Answer 1

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Moment of Inertia

• No, it goes down 4 times as much

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Moment of Inertia

• the front wheel of a bicycle is three times as
  large as the rear wheel. How much more massive
  must the rear wheel be to have the same moment of
  inertia as the front wheel?
• Answer 2

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Moment of Inertia

• the mass needs to be 9x the weight of the front
  wheel

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Moment of Inertia

• Mr. Lowe hangs a bowling ball that has a mass of
  14kg on a rope that is 10m long. Calculate the
  moment of inertia.
• Answer 3

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Moment of Inertia

• 1400kgm2

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Moment of Inertia

• Billy wanted to build a really fast cart, but he
  had to have a specific mass and radius of his
  wheels. In order to gain the greatest speed how
  should he build his wheels?
• Answer 4

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Moment of Inertia

• He should distribute the mass throughout the
  wheel, making a solid wheel.

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Moment of Inertia

• A strong man swings a 16-lb bowling ball around
  his head. The string attached to the ball is 3.7
  m long. What is the moment of inertia caused?
• Answer 5

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Moment of Inertia

• 99.5 kg m2

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Angular Momentum

• An 80 kg man is sitting at his swivel office
  chair and is spinning at a constant speed, he has
  a 2 kg coffee mug in his outstretched hand and he
  pulls it in to take a sip. How fast does he spin
  if his .5 m arm is pulled in to .1 m, and he was
  originally spinning at 1m/s?
• Answer 1

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Angular Momentum

• 5m/s

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Angular Momentum

• A 22 cm diameter basketball that weighs 11
  Newtons rolls down a hill at 17rps. What is the
  basketballs angular momentum?
• Answer 2

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Angular Momentum

• 1.5 kgm2

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Angular Momentum

• Is it possible for two objects with the same mass
  and same rotational speeds to have different
  values of angular momentum?
• Answer 3

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Angular Momentum

• Yes, if their radii are different.

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Angular Momentum

• Mr. Lowe swings a 2kg tennis ball in a circle at
  10m/s. The ball is attached to a piece of string
  that is 5m. Calculate the angular momentum of the
  tennis ball.
• Answer 4

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Angular Momentum

• 100m/s2

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Angular Momentum

• Why do we balance on a bicycle when it is moving?
  Answer 5

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Angular Momentum

• We balance, because the wheels have angular
  momentum and therefore a greater torque is
  required to change the direction of angular
  momentum.

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