Motion

Describing MotionMotion – when an object changes its position relative to a reference pointDistance – how far an object movesDisplacement – how far an object moves in reference to the starting point

Rates

Any change over time

Examples:$7.50/hrRpm (rotations per minute)Accidents/monthMiles/hrm/s

Speed / Velocity

Distance traveled per unit of time

Speed = distance / time

Speed describes the rate of motion

Velocity includes the rate of motion and direction

Speed

Speed that doesn’t change over time is constant speed

Most speeds are non constant average speed

Why can’t you run at a constant rate?

Average and Instantaneous Speed

Average speed is taken when speed is variable.

Average speed = total distance / total time

Instantaneous Speed = speed at any given point in time

Distance vs. Time Graphs

Visual representation of an object’s motion

Plot distance on the vertical axis (y-axis)

Plot time on the horizontal axis (x-axis)

Which is the independent variable?

Which is the dependent variable?

What does this graph represent?

AGENDA 1/19/11You will need your textbook for the assignment today

Access Chapter 2 Notes from my public folder

Acceleration Discussion

Ch. 2 Handout

AccelerationAcceleration is a change in the motion of an object.

Positive acceleration – velocity is increasing

Negative acceleration – velocity is decreasing

Changing an object’s direction is also accelerating

YOU CAN FEEL ACCELERATION

Calculating Acceleration

Acceleration = change in velocity / time

A = ΔV / t

(VF – VI)

___________

t

Acceleration

Unit of acceleration is m/s2.

A velocity vs. time graph

Which is the dependent variable?

Which is the independent variable?

(+) acceleration has a positive slope

(-) acceleration has a negative slope

Where is acceleration experienced at an

Amusement Park?

Newton’s Laws of Motion

1st Law- “an object in constant motion remains in constant motion until acted upon by an outside force.”

The law of inertia

2nd Law- F = ma

3rd Law- “for every action there is an equal and opposite reaction.”

ForcesForce- a push or a pull exerted from one object to another

Balanced Forces- forces acting on an object are all equal and in opposite directions

Unbalanced Forces- the magnitude and direction of the forces do not cancel one another out

Causes motion