CHAPTER 11 MOTION Section 1 Distance and Displacement Notes 11-1

Vocabulary Frame of reference Relative motion Distance Vector Resultant vector

Frame of Reference Objects that are not moving with respect to one another When looking at an object, like a butterfly, you need to have a background object to measure its speed by. Relative motion: Movement in relation to a frame of reference Ex: A train full of people People outside the train on the platform will have a different view of speed than people on the train. You need a meaningful frame of reference to determine true speed.

Measuring Distance Length of a path between two points Units used should be best suited to the motion you are studying SI Units for distance is meter (m) Longer distances might need something bigger km Light-year Shorter distance need something smaller cm mm

Measuring Displacements Displacement: the direction form the starting point and the length of a straight line from the starting point to the ending point. Used when giving directions “Walk 5 blocks north from the Post Office” Think about a roller coaster After completing one trip around the track, a car’s displacement is 0.

Combining Displacements Displacement is an example of a vector Vector: quantity that has magnitude and direction Magnitude can be: size, length, or amount Arrows represent a vector The length of the arrow shows magnitude Add displacements using vector addition. When two vectors are going in the same direction, you can add vectors. When they are going in opposite directions, you subtract.

Adding Vectors

Combining Displacements If displacement is not a straight line Must graph Then add up the vectors. Resultant vector: Vector sum of two or more vectors It shows displacements Points directly to the ending point

Resultant Vector

CHAPTER 11 MOTION Section 2 Speed and Velocity Notes 11-2

Vocabulary Speed Average speed Instantaneous speed Velocity

Speed Ratio of the distance an object moves to the amount of time it moves SI units = m/s (meters per seconds) Make sure to use the units that make the most sense to the speed your are messuring Two ways to express speed Average speed: for the entire duration of a trip Instantaneous speed: at a particular instant

Speed Average Speed: (ν) Total Distance Traveled/Total Time ν= d/t Instantaneous Speed: (ν) Ex: use the car’s speedometer Rate at which an object is moving at a given moment in time

Graphing Motion Distance-time graph Slope of a line on a distance-time graph is speed. Slope = change in distance/change in time Faster the speed of the object = steeper slope Slower the speed of the object = flatter slope If the line is straight at an angle, it shows constant speed If the object stops, the line will be flat.

Distance Time Graph

Velocity Speed and direction in which an object is moving Velocity is a vector. Cheetah chasing its prey It will change direction and speed as it chases Vectors would point in different directions according to where it moves The length of the vectors would signify its speed at that instant Longer vectors are faster Shorter vectors are slower Changing velocity can change just direction or just speed or both.

Combining Velocities Add two or more velocities by adding vectors Just like you practiced before If the vectors are 5 km/h and 12 km/h in the same direction, you add the two together Total velocities = 17 km/h

CHAPTER 11 MOTION Section 3 Acceleration Notes 11-3

Vocabulary Acceleration Free fall Constant acceleration Linear graph Nonlinear graph

What is Acceleration? Velocity changes frequently Ex: basketball game The ball is being passed quickly to a player. Then it is dribble by another player after it has been stolen. Then it moves at a different velocity when it is shot at the basket. The ball isn’t the only thing changing. The players are changing their velocity constantly also. Acceleration: Rate at which velocity changes Changes in speed, changes in direction or changes in both It is a vector

What is Acceleration? Changes in speed Often acceleration is used when an object is speeding up. However, in science, acceleration can be speeding up or slowing down. Ex: riding a bus You can feel the acceleration after a student is picked up at their stop and the bus takes off again. You can also feel the deceleration as the bus slows to stop at the next bus stop. Units: meters per second per second (m/s/s) or (m/s 2 )

What is Acceleration? Free Fall: Movement of an object toward Earth solely because of gravity Objects falling on Earth accelerate downward at a rate of 9.8 m/s s For each second it is in free fall, its velocity increases by 9.8 m/s t = 0 s; v = 0 m/s t = 1 s; v = 9.8 m/s t = 2 s; v = 19.6 m/s t = 3 s; v = 29.4 m/s

What is Acceleration? Changes in Direction Speed is constant Acceleration can change by changing direction Ex: carousel Constantly accelerating by changing direction Changes in Speed and Direction Like when riding a roller coaster Constant Acceleration A steady change in velocity Ex: a jet plane during takeoff

Calculating Acceleration Acceleration = Change in velocity / Total time Change in velocity = (final velocity – initial velocity) If velocity increases, acceleration is a positive number If velocity decrease, acceleration is a negative number Remember: Acceleration is changing when there is a direction change You don’t have to change the velocity to get a change in acceleration

Graphing Accelerated Motion (linear graphs) The slope of a speed-time graph is acceleration. Slope = change in speed / change in time Speed-Time Graph (linear graphs) Constant acceleration is shown with a straight line. Positive acceleration is pointing up to the right. Negative acceleration is point down to the right

Graphing Accelerated Motion Distance-Time Graph Accelerated motion is shown by a curved line Ex: a ball being dropped to the ground The slope of the curved line changes as the seconds tick The slope at the beginning is less than the slope at the end. An increasing slope means and increase in speed. An increase in speed means the ball is accelerating. Instantaneous Acceleration How fast a velocity is changing at a specific instant

Distance-Time Graph