Motion. Motion: The change in position of an object as compared with a reference point Reference point: System of objects that are not moving (stationary)

Chapter 2Motion

Motion: The change in position of an object as compared with a reference point

Reference point: System of objects that are not moving (stationary) in respect to one another

2.1 Distance and Displacement

Distance

Length of path between 2 points

May not be straight line (shortest path)

Units: meters (m), km, miles, cm, etc.

Ex: Roads/streets we drive

Displacement The direction and

length in a straight line from start to end

ALWAYS includes direction from start point

Ex: walk 5 blocks north from McDonald’s

Ex: roller coaster ride displacement = 0

How fast in a given amount of time1. Distance traveled by object2. Time to travel that distance Units:

◦ m/s◦ mi/hr or mph◦ km/hr

Speed

Average Speed - Calculated speed for trip Ex) Ran marathon at 6 mi/hr

Instantaneous Speed - speed at exact moment Ex) speedometer reading = 55 mi/hr

Object going an equal distance in equal amounts of time = Constant speed (not speeding up or slowing down)

Speed Types

Doesn't tell the direction45 mph4 m/s

Speeds

Expressed in m/s Speed = Distance/Time Or S = d/t Ex: A car traveling at a constant speed and

it goes and distance of 645 m in 25 s. What is the car’s speed?

S = d/t S = 645m/25s S = 25.8 m/s

Calculating Speed & Avg. Speed

Graphs show speed/velocity Time (independent variable) -> x-axis Distance (dependent variable) -> y-axis

Distance - Time Graphs

Distance - Time Graph

Distance -Time Graphs

Slope of line = speed or velocity

Straight line = constant speed (cruise control)

Steeper slope = faster speed

Distance - Time Graphs Horizontal (flat)

line = object not moving

Exs: stopped at red light, parked, at store

Distance - Time Graphs

Negative slope = went backwards (neg. displacement)

Ex: went to store, shopped, and back home

Velocity

Measurements: Speed: m/s,

km/h, or m/h

Direction: N (NE, NW), S

(SE, SW), East, and West

Describes both speed and direction of motion

Must give how “fast” and direction the object is going

Ex: 45 km going South

Can be described as changes in speed, direction, or changes in both

Small value = increasing gradually

Larger value = speeding up more rapidly

The slope of a speed-time graph is acceleration

2.2 Acceleration

Positive Acceleration – velocity increases or speeds up (gives a positive slope )

Negative Acceleration – velocity decreases or slows down (gives a negative slope )

Horizontal line – on a velocity-time graph; stays constant, velocity does not change (-----)

Acceleration (pg. 49 -50)

Any change in how fast or change in direction

Speed up Slow down Turn a corner Go around a curve

Changes in Acceleration

Acceleration = change in velocity/time

a = (final velocity – initial velocity)/time

Measured in meters/second/second

a = vf - vi/t

Calculating Acceleration

Calculating positive acceleration = pos. # (speeding up)

Ex: a = (80m/s – 0m/s)/20s = 4m/s

Calculating negative acceleration = neg. # (slowing down)

Ex: a = (0m/s – 3m/s)/2s = 1.5 m/s

Calculating Acceleration

Causes velocity change Unit = Newton (N) Net Force - combo of all forces acting on object

Net force = 0Either stopped or constant speed

Force

2 Types of forces:

1. Balanced Forces - net force = 0 Forces cancel out Ex) Fair tug of war

2. Unbalanced Forces - net force not = 0 One force is stronger Car vs Train

Force

Balanced Forces

Unbalanced Forces

Physicist who described relationship between force & motion

3 Laws: Newton’s Laws of Motion

Isaac Newton

AKA – Law of Inertia “An object at rest stays at rest, and an

object in motion stays in motion, unless acted upon by an unbalanced force.”

Inertia = tendency of object to stay at rest Exs: car crashes, magician table cloth trick

Newton’s 1st Law

1st Law