MOTION

Chapter 11

How do you know something is moving?

Depends on your frame of reference.

A frame of reference is the location from which motion is observed.

Most common: the earth.

Measuring distance

Distance: the length of a path between two points. Considered a scalar quantity. (only a magnitude) Can be expressed in any number of units. Choose a unit that is best suited for the motion

being described. Examples: meters, kilometers, centimeters

Measuring displacement

Displacement is independent of the path taken by the object.

Involves the starting point, ending point, and direction. Vector quantity

Example:

Adding vectors When the vectors are

along the same plane they are added arithmetically.

Many different methods for adding vectors that do not lie in the same plane.

Examples on board

What is SPEED ?

The ratio of distance an object moves to the amount of time it takes to move that distance.

How fast or slow an object is traveling. Is speed a vector or a scalar quantity

Average Speed

Defined as the total distance / total time. Or

= d/t

Example problems on page 333

Instantaneous speed

Not as useful in physical science. Much more difficult to calculate.

Defined as the speed at a given moment in time.

Graphing motion

Distance-time graphs. The slope of a line on a

distance-time graph is the speed.

At what speed is the student walking down the hallway?

Speed vs velocity

Velocity is speed in a given direction.

MUST have a direction.

Considered a vector quantity

What is acceleration?

A situation in which the velocity is changing. “Speeding up or slowing down” “changing direction” Science definition: the rate of change of velocity Can be both negative and positive Acceleration is a VECTOR quantity.

Acceleration examples:

Which car is experiencing acceleration?

If you said the red and blue car you were right!

A distance-time graph of all three cars:

The distance-time graph for accel. Is always a curve.

What is the formula for acceleration?

Acceleration = final velocity – original velocity

time

Or the change in velocity ( v) / change in time (t)

Label : m/sec/sec or m/sec2

Example problems:

A roller coaster’s velocity at the top of a hill is 10 m/sec. Two seconds later it reaches the bottom of the hill with a velocity of 26 m/sec. What is the acceleration of the roller coaster?

More examples:

A roller coaster is moving 25 m/sec at the bottom of a hill. Three seconds later it reaches the top of the hill and is traveling at a speed of of 10 m/sec. What was the roller coaster’s acceleration?

Can you have negative acceleration? YES. The negative sign tells us the direction of the

acceleration, usually means deceleration.

Free Fall

Acceleration due solely to the force of gravity.

All objects fall at the same rate.

9.8 m/sec2

Graphing acceleration

Distance-time graph for constant acceleration always a CURVE.

Velocity-time graph for constant acceleration always a STRAIGHT LINE.

Example graphs:

Assignment:

Pages 351-3531-10, 17,18,19,20,21,24,29,301-5 page 353