9-1 9-2 9-3 location. concept development 9-1 created for cvca physics by dick heckathorn 4 january...

9-1

9-2

9-3

Location

Concept Development 9-1

Created for CVCA PhysicsBy

Dick Heckathorn4 January 2K + 5

Circular Motion

a. If there is no relative motion between the train and the edge of the platform, how fast must the train move compared to the rim speed of the rotating platform?

Circular Motion

b. Why is the stairway located at the center of the platform?

White Water Landing

Circular Motion

a. How is the size of the round platform and train speed related to the amount of time that passengers have for boarding?

Circular Motion

b. Why would this rotating platform be impractical for high speed trains?

Circular Motion

a. The platform is not rotating on its axis and the people are at rest.

Circular Motion

b. When the platform rotates, the person in the middle stands as before. The person at the edge must lean inward as shown.

b. Make a sketch of the missing people to show how they must lean in comparison.

The sketch on the right shows the container rotating about a central axis at constant speed.

Make a sketch showing the orientation of the other two ducks with respect to the water surface.

Circular Motion

The sketch on the left shows some toy ducks floating on the water.

Circular Motion

The sketch on the left shows the water surface when the tire is not rotating.

The sketch on the right show the water surface when the tire and water rotate about its central axis.

Circular Motion

Now suppose the tire is rotating about the same axis while orbiting in outer space.

Draw the shape of the water surface in the cross-sectional view above.

Scale up the rotating tire model to a rotating space habitat orbiting in space.

Where would the people be and how would they be affected?



Dick Heckathorn15 December 2K+3

a. Your body lurches: backward

b. The car accelerates: forward

c. Force on car acts: forward

You’re in a car at a traffic light. The light turns green and the driver steps on the gas.

Accelerating & Circular Motion

v

a

a. Your body lurches: forward

b. The car accelerates: backward

c. Force on car acts: backward


You’re driving along and approach a stop sign. The driver steps on the brakes.

v

a

a. Your body leans: outward

b. Direction of acc. is: inward

c. Force on car acts: inward


You continue driving and round a sharp curve to the left at constant speed.

va

the same not related opposite


4. In general, the directions of lurch and acceleration, and therefore the direction of lurch and force are:


a. If it moves faster, its direction changes: faster slower

b. This indicates that as the speed increases, acceleration:

increases decreases stays the same

5. The whirling stone’s direction of motion keeps changing.

b. This indicates that as the radius decreases, acceleration:

increases decreases stays the same

a. For a given speed, the rate that the stone changes direction is: less more the same


6. Consider whirling the stone on a shorter string – that is, of smaller radius

Centripetal Force p 40

1. A rock tied to a post moves in a circle at constant speed on a frictionless horizontal surface. All the forces acting on the rock are shown.

Fearth on rock

Ftable on rock

Fstring on rock


a. The vector responsible for circular motion is: Fstring on rock

Fearth on rock

Ftable on rock

Fstring on rock

b. The net force on the rock is: Fstring on rock


2. The rock is tied to a string and swings in a circular path. It is not resting on a surface. No friction. Find the net force.

W

FequilibriumT

Fnet

Fearth on rock

Fstring on rock


a. What is the direction of Fnet? to center

W

T

Fnet

b. Does Fnet lie in plane of circular path? Y c. Is Fnet horizontal Component of T? Yes d. Is Fnet the centripetal force? Yes


3. The rock rides on a horizontal disk that rotates at constant speed about the vertical axis. Friction prevents the rock from sliding. Draw and label all vectors.

Fearth on rock

Fdisk on rock

Ffriction


Fearth on rock

Fdisk on rock

Ffriction

b. Which force is centripetal? Ffriction c. Which force provides net force? Ffriction

d. Why do we not say net force is zero?because centripetal acceleration is not zero


4. Now the rock is held in place by friction against the inside wall of the rotating drum. Draw and label all forces that act on the rock.

Fearth on rock

Ffriction

Fwall on rock


Fearth on rock

Ffriction

Fwall on rock

a. Which force is centripetal? Fwall on rock b. Which force provides net force?

Fwall on rock


5. The rock rests against a frictionless wall of the cone which rotates about its vertical axis. The rock does not slide up or down. Draw and label all forces on the rock.

Fearth on rock

FeFwall on rock

Fnet

a. Should Fnet lie in the plane of the circular path? Yes


Fearth on rock

Fwall on rock

Fnet

b. Why It provides the centripetal force for circular motion



Dick Heckathorn15 December 2K+3

1. From Bob’s point of view, he is at rest and sees Suzie moving:

clockwise counter clockwise

2. When Bob rides in the opposite direction as the habitat rotates, Suzie sees him moving:

faster slower

3. As Bob’s bicycle speedometer reading increases, his rotational speed decreases

and the normal force that feels the weight decreases.

So friction between the tires and the floor decreases.

4. When Bob gets his speed up to 30 km/hr, as read on his bicycle speedometer, Suzie sees him:

motionless

5. Bouncing off the floor a bit while riding at 30 km/hr, and neglecting wind effect, Bob:hovers in midspace as the floor whizzes by him at 30 km/hr.and he finds himselfin the same frame of reference as Suzie

6. Bob now rides in a clockwise direction, with the rotation of the habitat. Now Suzie sees him moving faster.

7. As Bob gains speed, the normal support force that feels like weight increases.

8. When Bob’s speedometer reading gets up to 30 km/hr, Suzie sees him moving 60 km/hr

and Bob finds himself:

pressed harder against the floor.

Next, Bob goes bowling. You decide whether the game depends on which direction the ball is rolled!

That’s all folks!

Bob is standing on a people mover (conveyor belt) at the airport which is moving toward the west at a speed of 6.0 m/sec.

Susie is standing to one side looking at Bob.

1. From Bob’s point of view, he is at rest and sees Suzie moving:

westward

eastward

not moving

2. Thus Bob sees Suzie moving at the same speed but in the

same

opposite

direction.

3. Bob starts walking to the east. Suzie will see Bob

speeding up

or

slowing down

4. As Bob walks faster and faster, Suzie sees Bob

speeding up more

or

slowing down more

5. When Bob gets his speed up to 6.0 m/s, Suzie sees him

moving at 6 m/s

motionless

moving at 12 m/s

6. Bob makes a slight push on the conveyer belt while walking at 6.0 m/s (east).

From Suzie’s point of view, he

will be moving towards the east

will be motionless

will be moving towards the west

7. Bob now finds himself

in the same frame of reference

moving west

moving east

relative to Suzie

8. Bob stops his eastward movement of a short time, thus not moving relative to the conveyor belt. He then starts walking towards the west. Suzie sees Bob

speeding up or slowing down

9. As Bob speeds up (walking to the west), Suzie sees Bob

speeding up or slowing down

10. Bob speeds up until he is walking at 6.0 m/s relative to the conveyor belt.Suzie sees Bob’s speed as6.0 m/s E motionless12.0 m/s W

11. Bob goes bowling on the conveyor belt. If the pins are set up so that he rolls the ball in a westerly direction, how should he alter his shot compared to the conveyor belt not moving?

none

12. Bob goes bowling on the conveyor belt. If the pins are set up so that he rolls the ball in a easterly direction, how should he alter his shot compared to the conveyor belt not moving? none

12.Bob goes bowling on the conveyor belt. If the pins are set up so that he rolls the ball in a northerly direction, how should he alter his shot compared to the conveyor belt not moving? None

9-1 9-2 9-3 location. concept development 9-1 created for cvca physics by dick heckathorn 4 january...

Documents

circular motionb

circular motionthe sketch

circular motionnow

rotating platform

water surface

constant speed

train speed

speed increases