Chapter 4

Linear Motion

You can describe the motion of an object by its position, speed, direction, and

acceleration.

Speed

Speed is a scalar.

Speed = Distance/Time

Hint: Remember the units for speed. Miles per hour A Distance over a time.

Velocity

Velocity is the vector form of speed.

Means that a change in direction is a change in velocity.

Instantaneous Vs. Average

Average speed is over a time period. Ex: Drove to LA in 5 hours. It’s 338 miles.

What was my average speed?

Instantaneous Speed: The speed at any one instant.

Ex: The speed the speedometer reads.

Acceleration Acceleration = velocity/time. Acceleration is a change in velocity over

time. Acceleration is a vector. The Units: m/sec2 distance/time squared

Question: Is a change in direction considered an acceleration?

How Fast do things fall on Earth?

Make it simple first.No Air resistance.

This is called Free Fall.Falling without air resistance.

Things accelerate at 10 m/sec2

This is the acceleration due to gravity. Remember this number from weight.

Objects in Free Fall

Graphs of Motion

Steeper the line the faster it is changing

Here the rate of change of distance is speed.

Slope of line--Rate of change.Rise over Run

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Motion is relative

Motion can only be described in relation to another object.

An object is moving if its position relative to a fixed point is changing.

Air Resistance

Air resistance slows objects that move through the air.

The faster the object moves, the more air resistance the object feels.

The amount of air resistance also depends on the shape of the object.

Terminal Speed

At some point during an object’s fall through the air terminal speed happens.

Point at which the air resistance equals the weight of the object

The net force becomes zero. No acceleration happens and thus the

object moves at a constant speed.

Friday Look Back Divide paper into 3 sections. I want 18 responses total

If you can’t think of 6 thingsfor each section then make more in a section that you can.

1. What did I know about this week’s material before this week?

2. What did I learn about in physics this week?3. What questions do I have about this week’s

material?