Warm Up 9Warm Up 9 9/12/11 9/12/11

How many significant figures are in 80900?

Warms up will be checked Wed.

TestTest

Curve was 5 points

Guaranteeing Partial Credit

1. Organize what the problem gives you

2. Make a drawing if necessary3. Identify the equation you will use4. Fill in the equation with the

givens5. Show your work6. Circle your answer with the

proper units

GradesGrades

Still behind in grading menus

Significant Figures and UnitsSignificant Figures and Units

Are required for correct answers from now on

Correct me

4 Rules to Significant Figures4 Rules to Significant Figures

Rule 1Rule 1

All non-zero digits are significant.

◦5 m◦76 m/s◦4567 m/s2

◦94586 N

Rule 2Rule 2

All zeroes between significant digits are also significant.

◦30,505 kg◦50,500 s◦50,000,005 m/s◦02020 m

Rule 3Rule 3

Zeroes to the right of a decimal or another significant digit are significant.

◦2.00 N◦570.090 J◦56.000 A◦500.

Rule 4Rule 4

Zeroes used to for spacing are NOT significant.

◦0.2 W◦0.002 V◦0.00200 km◦1.00200 km

When to useWhen to use

In problems, the least sig fig rules them all.

A car can accelerate from zero to 12 m/s in 4.65 seconds. What is its average acceleration?

When to useWhen to use

ONLY apply significant rules to the final answer◦Calculators are good at being accurate

A car can accelerate from zero to 12 m/s in 4.65 seconds. What is its average acceleration?

Kinematic ConceptsMotionRequires a change in distance/displacement

Change in distance/displacement must occur over a period of time (rate)

Difference Between Scalars and VectorsIn the end, does this sailboat

have a displacement?

Kinematic ConceptsAverage SpeedBasic motion = ∆d / ∆tSpeed is the rate of change of

distance◦Speed = change in distance

over time◦Formula:

savg = ∆distance / ∆time

Kinematic ConceptsAverage VelocityBasic motion = ∆d / ∆tVelocity is rate of change of

displacement◦Velocity = change in

displacement over time◦Formula:

vavg = ∆displacement / ∆time

Difference Between Scalars and VectorsA car is going due north at 60

km/hr.Another car is going due

south at 60 km/hr.Do the cars have the same

speed?Do the cars have the same

velocity?

Kinematic ProblemsSpeed and VelocityAn ostrich can run at speeds

of up to 72 km/h. How long will it take an ostrich to run 1.5 km at this top speed?

Perfect Physics World

One model of physicsNo friction or air resistance

Kinematic ConceptsAverage VelocityMotion = ∆d / ∆tSpeed is the rate of change of

distanceVelocity is rate of change of

displacementVelocity and speed tell you how

fast position is changing, not just a change in position.

Average velocity = ∆d / ∆t

Kinematic Vocabulary

Average Velocity◦Can velocity be higher or lower

than average over the same period of time?

Instantaneous Velocity◦An object’s velocity at a specific

moment in timeConstant Velocity

Warm Up 10 9/13/11

Estimate the velocity the chair you are sitting on.

Hint: There are at least 3 velocities.

Frame of Reference

“Frame of Reference” is similar to “point of view”

Motion is relative to the Frame of Reference

0 m/s

4 m/s

2 m/s

5 m/s

Your Frame of Reference is considered 0

Objects going in opposite directions – Add

Objects going in the same direction - Subtract

Practice Problem

What is the relative speed of 2 cars heading towards each other if one car is traveling 12 m/s and the other is 33 m/s?

What is the relative speed if the fast car was trying to pass to slow car?

Kinematic Vocabulary

Displacement is change in position

Velocity is change in displacement over time

Acceleration?

Kinematic ConceptsAccelerationAcceleration is the rate of

change in the magnitude AND/OR direction of velocity.

Acceleration occurs when:◦Speed (magnitude) increases or

decreases◦Velocity changes direction

Average Acceleration

2if

avg

aa

t

va

Is there acceleration?From a dead stop, a car hits the

gas and goes 100 m in 3 s.A car moves at a constant

velocity of 10 m/s. Ahead, a cat starts to cross the street. The car hits the brakes!

A car is driving around in a perfect circle at a constant speed.

Water drips from the ceiling at one drop per second. As the drops fall, what is their relative distance?

Is the distance between 2 drops the same, increases or decreases?

2if

avg

aa

t

va

t

dvavg

How acceleration changes motion.

Accel.VelocityDisplace-ment

t=0

t=1s

t=2s

t=3s

t=4 s

Practice Problem

A car drives for 1 hour at 20 km/h. Then it drives for 1 hour at 30 km/h. What is the average speed of the car?

Did the car undergo any acceleration?

Kinematic ProblemsSpeed and VelocityIf Hawaii is 2.24 x 103 km long

and the moves at an average speed of 50. mm per year, how many years would it take to move the length of Hawaii?

Kinematic ProblemsSpeed and VelocityJupiter, the largest planet in

our solar system, has a radius of about 7.1 x 104 km. Its period of rotation, however, is only 9 h, 50 min. Calculate the average speed (in km/hr) for one rotation. What is the average velocity?