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.

Frames of Reference How fast are you moving right now? - Tucker Hiatt http://ed.ted.com/lessons/how-fast-are-you-moving-right-now-tucker-hiatt

Concept Questions A police car is chasing a criminal car. The police car is moving at 30 m/s and the criminal’s car is moving at 20 m/s. What is the speed of the police relative to the criminal? The police car is currently 1000 m behind. How long will it take for the police to catch up to the criminal?

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

Pythagorean Theorem

Concept Questions What is the displacement?

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 scalar

Average Speed  = d/t Defined as the total distance / total time. Or 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?

Lab – Graphing x vs t Marble falling through shampoo

Speed vs velocity Velocity is speed in a given direction. MUST have a direction. Considered a vector quantity

Concept Question If the boat is moving at If the boat is moving at 40 m/s across, and the river is flowing down at 30 m/s, what is the speed of the boat relative to the shore?

What is a vector? - David Huynh http://ed.ted.com/lessons/what-is-a-vector-david-huynh

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

Brian Cox visits the world's biggest vacuum chamber - Human Universe: Episode 4 Preview - BBC Two https://www.youtube.com/watch?v=E43-CfukEgs

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

Example graphs: