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 .

Newton’s second LawNewton’s second Law

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 .

Newton’s second LawNewton’s second Law

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.

Newton’s third LawNewton’s third Law

Body A Body B

Force on B by AForce on A by B

Newton’s third LawNewton’s third Law

Circular Motion in horizontal circlesCircular Motion in horizontal circles

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

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 ?

Vertical circular motion Vertical circular motion Bucket and waterBucket and water

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

Vertical circular motion Vertical circular motion Bucket and waterBucket and water

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

Fc = T + mg

Tension T Weight mg

Vertical circular motion Vertical circular motion Bucket and waterBucket and water

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

Fc = T - mgTension T Weight

mg

Vertical circular motion Vertical circular motion Bucket and waterBucket and water

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

Fc = R + W Reaction of the bucket

R

Weight of water

W

Vertical circular motion Vertical circular motion Bucket and waterBucket and water

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

Fc = R - W

Reaction of the bucket

R

Weight of water

W

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

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