MOTION Chapter 9

SECTION 9-1 Describing & Measuring Motion

Recognizing Motion An object is in motion when its distance from another object is changing.

Frame of Reference - the background or object used for comparison to tell if an object is in motion. The most common frame of reference is the earth.

This is Fred Astaire - a famous actor & dancer This is Fred Astaire - a famous actor & dancer. Where is he dancing in this movie? How can you tell?

Reference point - an object is in motion if it changes position relative to its reference point.

Describing Distance To describe motion, you need units of measurement. In the metric system, these are meters.

Speed The distance an object travels in a certain amount of time.

Constant Speed Speed that does not change during the motion of an object.

Average Speed - when there is a change in the speed of an object. Total distance divided by total time = average sped.

Velocity - speed in a given direction (When both speed & direction are known.)

Graphing Motion You can show motion as a line graph. - plot distance against time. X axis = time (horizontal) y axis = distance (vertical) (x,y) = location of an object at a particular time.

Slope of a Line Slope = steepness, or slant of a line - tells you how fast one variable changes in relation to the other variable - the faster the motion steeper the slope

Calculating Slope The slope of a line is its rise divided by its run. (Choose two points on the line.) The rise is the vertical difference between the two points. The run is the horizontal difference between the two points.

The slope is 2 m/s - which means the that the speed of the moving object is 2 meters every 1 second. - this is a constant slope

y =2x represents the line containing the 2 variables. X = time y = distance - so each second the object moves 2 meters If the speed of the object were 5m/s then the equation of the line would be y = 5x

Section 9-2 Slow Motion on Planet Earth Some motion is very slow. The plates that cover the earth’s surface move maybe 5 cm a year.

Earth’s Tectonic Plates The movement of earth’s crustal plates causes earthquakes, volcanoes, mountain building.

Section 9-3 Acceleration Acceleration is the rate at which velocity changes. - refers to: - increasing speed - decreasing speed - changing direction

Increasing Speed Any time the speed of an object increases, the object experiences acceleration.

Decreasing Speed When an object’s motion slows down. - deceleration or negative acceleration

Changing Direction Remember: Velocity involves both speed & direction. -So acceleration occurs even if the speed stays the same rate BUT the direction of motion changes. -ex. A car turning a corner or an object moving in a circular path.

Circular Motion Orbits of planets, satellites, space craft, etc. are circular motions.

Circular Motion So if you are moving at a constant speed on this ride, you are still accele- rating because-???

Circular Motion Because your direction is changing.

Acceleration To determine acceleration, you must calculate the change in velocity during each unit of time.

Acceleration Measured in units of: distance/time/time - km/s/s or km/s2 - m/s/s or m/s2

Change of speed over time - ACCELERATION

Graphing Acceleration Shows a change in speed over time.

Graphing Acceleration Constant Speed Acceleration - a linear relationship - a nonlinear relationship

Graphing Acceleration Linear relationship - a straight line graph shows speed is constant Nonlinear relationship -a graph that shows distance versus time (a curved line) -as speed increases the graph curves upward.

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