M OTION AND FORCES CHAPTER 1 Science Ms. Curd

P OSITION Definition: The location of a place or object When you identify the position of an object you are comparing the location of the object with the location of another object or place In your notebook: choose an object in the classroom and describe its location What kind of information do you need?

R EFERENCE P OINT Definition: A location to which you compare other locations Cities, houses, streets, landmarks Longitude and Latitude are a standard reference point Makes it easier for people to compare locations In your notebook: Describe our school in terms of reference point

M EASURING D ISTANCE Depends on the information you want Do you want the straight line distance? Or the total length of a path between two positions? Scientists use a standard unit of measurement Standard Meter (m) equals 3.3 feet Longer distances are measured in Kilometers (km) equals 0.62 miles Shorter distances are measured in Centimeters (cm) equals 0.39 inches

M OTION Definition: Change of position over time Horizontal and vertical positions change Even if you missed the motion you would know that motion occurred How? The distance between the starting and ending positions would have changed

D ESCRIBING M OTION Speed: a measure of how quickly or slowly an object changes position Faster object moves farther than a slower in the same amount of time Described by using a frame of reference-the location of an observer who may be in motion You are on a bus and pass a stop sign, you may say the driver is not moving (not changing position compared with the inside of the bus) but the stop sign is (moving past the observers window Someone on the sidewalk might say the driver is changing position where the street sign is not

Speed Definition: a measure of how fast something moves or the distance it moves, in a given amount of time Greater the speed = faster it changes position Rate: The way in which one quantity changes compared to another quantity Speed = the rate at which the distance an object moves compared to time Riding a bike to the movies Running late? Pedal harder to increase rate your distance changes

Calculating Speed Need to know distance and time Calculated by dividing distance an object travels by the time it takes to cover the distance Formula: Distance D Speed = S = TimeT Speed (S), Distance (d) and Time (t) Shows how distance, time and speed are related Standard Unit: meters per second (m/s) Also: kilometers per hour (km/h) Miles per hour (mi/h or mph)

AVERAGE SPEED Speed is not constant Instantaneous speed = the moment to moment speed Average of your time over a distance Running a 1600 meter race; take the time from each of the four laps and add them together; divide total distance by total time Distance-Time graphs Plots distance against time Shows how speed relates to distance and time Shows how distance and speed change with time Time is the horizontal axis (x-axis) Distance is the vertical axis (y-axis) Page 21 in book

V ELOCITY Definition: a speed in a specific direction Walking east at a speed of three meters per second describes velocity Someone walking north at three meters per second has the same speed but not the same velocity Change in speed or direction = change in velocity If you slow down but head in the same direction your velocity changes If you change direction but stay at the same speed your velocity changes Average calculated differently for velocity than for speed Average speed depends on the total distance you traveled Average velocity depends on the total distance you are from where you started If you travel north 30 km/h and then south at 30 km/h average speed is 30 km/h BUT average velocity is 0 km/h because you ended up where you started

V ECTOR Definition: a quantity that has size and direction Speed is NOT a vector Speed only has size, not direction Velocity IS a vector Has size (the speed) and direction

ACCELERATION Definition: the rate at which velocity changes with time Measure of how quickly the velocity is changing No change in velocity = no acceleration IS a vector, has size and direction Direction of acceleration determines whether an object will slow down, speed up or turn Acceleration in the same direction = object speeds up Acceleration in opposite direction = object slows down (negative acceleration) Acceleration at a right angle = direction of motion changes

C ALCULATING ACCELERATION Need to know how velocity changes with time Change in velocity found by comparing the beginning velocity with the final Time interval over which velocity changes can be measured Formula: final velocity – initial velocity acceleration = time Standard unit of measure: meters per second over time, meters per second per second

Warmup: Decide if these statements are true. If they are not true, correct them. (Copy question in notebook) 1. Speed includes direction, while velocity does not. 2. A moving object covers the same distance in less time if its velocity is greater. 3. Acceleration measures only change in speed.