Physics day5b

PHYSICSPSHS 3RD YEAR

Session 5

TUTORIAL REMINDERS

• 2 Hours today• Be ready with your:

– Sci. calculator– Physics notes– Session 4 handout– Paper– Pen

• Today’s Flow:• CIRCULAR MOTION

1.) Review of terms

2.) Pinoy Henyo

3.) Self-check exercises

4.) Challenge exercises

Answers: Terms

1. Directed radially toward the centerCENTRIPETAL

2. Constant speed along a straight line

UNIFORM VELOCITY

3. Angular displacement divided by time t

ANGULAR VELOCITY

Answers: Terms

4. The direction of the linear velocity of an object in circular motion

TANGENTIAL

5. Movement of an object in a circle experiencing uniform speed

UNIFORM CIRCULAR MOTION

6. Directed distance (distance where direction is important)

DISPLACEMENT

Answers: Terms

7. What is done to curved roads to reduce skidding

BANKING

8. What an object experiences when there is a change in the magnitude of its velocity (speed), or a change in its direction of motion

ACCELERATION

Circular Motion

distance circumferenceAverage speed = =

time time2

= R

T

Does an object in uniform circular motion have constant

velocity?No. Constant speed

but constant changing direction of motion. Thus, velocity is NOT constant.

Uniform Circular Motion• Since the object is in constant speed BUT

continuously changing direction – there is acceleration.

What causes this acceleration and movement in a circle?

The NET FORCE is directed towards the center, and keeps the object in a circular motion.

Answer page 3 Centripetal Force #s 1-5,Page 4 problem 4.

2

,radial accelerationR

va

R

RFF

Non-Uniform Circular Motion

If the net force is NOT directed towards the center but at an angle, the net force has 2 components!

• EX.4 (page 111, Giancoli)• A 0.150-kg ball on the end of a 1.10m-

long cord (negligible mass) is swung in a VERTICAL CIRCLE. Determine the minimum speed the ball must have at the top of its arc so that the ball continues moving in a circle.

What’s the difference?• CENTRIPETAL

FORCE FR

– Keeps object moving in a CIRCLE

• TANGENTIAL FORCE Ftan

– Acts to INCREASE or DECREASE the speed of the object

2

,

radial acc'n

R

va

R

tan ,

tangential acc'n

va

t

Non-Uniform Circular Motion

• TANGENTIAL acceleration – the direction of the tangential acceleration is in the direction of the change in velocity

tan

va

t

Non-Uniform Circular Motion

Total vector acceleration a

Magnitude of total vector a

Direction of total vector a

tan Ra a a �������������������������� ��

2 2tan Ra a a

Resultant vector of aR and atan

A race car starts from rest in the pit area and accelerates at a uniform rate to a speed of 35 m/s in 11 sec, moving on a circular track of radius 500m. Assuming constant tangential acc’n, find a.) Tangential acc’nb.) Radial acc’n, at the instant when the speed v is 15 m/s.

Law of Universal Gravitation

(Adapted from Page 119, Giancoli)

Tyrone and Mia have masses of 50 kg and 75 kg respectively. They sit 1.0 m apart in the front center of their Physics class. Estimate the magnitude of the gravitational force each exerts on the other.

1 22

m mF G

r

ROTATIONAL MOTION

Rotational Motion

• All points in the object move in circles.• The centers of these circles all lie in a line

called the axis of rotation.

• Where

lr

angle measure subtended by arc lengthradius

llr