Circular Motion

transcript

PhysicsPhysics

Circular Motion

CircularCircular motionmotion

• Revision

• Circular motion in horizontal

• Vertical circular motion

• Loop-the-loop

RevisionRevision

• Newton’s Laws

• Circular motion in horizontal circles

• Centripetal force and acceleration

• Angular velocity, frequency & linear velocity

Newton’s first LawNewton’s first Law

A body continues in a state of

rest or uniform motion in a

straight line unless it is acted

upon by external forces.

No external forceThe body remains at rest.

The body moves with a constant speed.

Newton’s first LawNewton’s first Law

The rate of change of momentum

of a body is proportional to and

in the same direction as the

resultant force that acts on it.

constant is m if ma F dt

(mv) d F net

Newton’s second LawNewton’s second Law

For fixed forceA body with a larger mass moves with a smaller acceleration .

A body with a smaller mass moves with a larger acceleration .

For fixed massA body with a smaller net force moves with a smaller acceleration .

A body with a larger net force moves with a larger acceleration .

If one body exerts a force on

another, there is an equal and

opposite force, called reaction,

exerted on the first body.

Newton’s third LawNewton’s third Law

Body A exerts a force on body B, then body B exerts an equal and opposite force on body A.

Body A Body B

Force on B by AForce on A by B

Circular Motion in horizontal circlesCircular Motion in horizontal circles

Angular velocity = / t

Linear velocity v = r Centripetal force

F = m r 2 = m v2 / r

Centripetal accelerationa = r 2 = v2 / r

Circular Motion in horizontal circlesCircular Motion in horizontal circlesConical pendulumConical pendulum

Do you remember what kind of forces provides the centripetal force to the bob ?

Tension T

Weight mg

Centripetal force

Vertical circular motion Vertical circular motion Bucket and waterBucket and water

Does the water spill out the bucket when whirling ?

If no, why doesn’t it spill out ?

What kind of motion does thebucket perform ?

Vertical circular motion

What kind of force provides the centripetal force Fc to thebucket ?

Tension T

Weight mg

What kind of force providesthe centripetal force Fc to the bucket at the highest position ?

Fc = T + mg

Tension T Weight mg

What kind of force providesthe centripetal force Fc to the bucket at the lowest position ?

Fc = T - mgTension T Weight

What kind of force provides the centripetal force Fc to the water at the highest position ?

Fc = R + W Reaction of the bucket

Weight of water

What kind of force providesthe centripetal force Fc to the bucket at the lowest position ?

Fc = R - W

Reaction of the bucket

Weight of water

Vertical circular motion Vertical circular motion Loop-the-loopLoop-the-loop

What kind of force providesthe centripetal force Fc to the mass ?

The reaction of the track

M.C. Exercise

Class Class exercisesexercises

Mainmenu

True or False

M.C. Question 1

Which of the following formula

shows Newton’s second Law ?

v = r = / tF = maa = v2 / r

M.C. Question 2

At which position is the tension

on the bucket largest ?

True or False Question 1

True False

If the angular velocity of the bucket

at the top position is too small,

water may spill out.

True False

In the Ocean Park , cart coast rider

can loop the loop by tension.

True or False Question 2

Circular Motion

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