Chapter 2

Models & Acceleration

Types of Speed• 1. Average Speed- total distance traveled

divided by the total time taken• 2. Speed (Instantaneous)- speed at a specific

point in your journey– Ex) Looking at the speedometer

Types of Models:

• 1. Physical- Look, touch, feel, & take measurements from– Scale- model is proportional to real object – Ex: A scale of 1 inch=10 feet, • Means every inch on the model = 10 feet in real life

2. Conceptual- describe how a concept works– Ex: the design of an atom, or how the earth and

planets orbit around the sun

• 3. Graphical- Shows relationship between variables on the x-axis and y-axis– Dependent (y)– Independent (x)

Cause and Effect Relationships

• Changing one variable (x) affects another (y)

• Best seen in graphs = Good way to see connections between two variables

Types of Relationships• 1. Strong Relationship-– small change in one makes a big change in

another– Often ‘positive’ slope

• 2. Weak Relationship-– Big change in one variable has little effect on the

other– Line looks flat

• 3. Inverse Relationship-– One variable increases, the other decreases– Often ‘negative’ slope

Dimensional Movement

• One Dimensional– Speed, linear equations, walking, free falling– Direction along one plane (horizontal OR vertical)

• Two Dimensional– Velocity, vectors, acceleration, objects moving at

angles – Direction in vertical AND horizontal – It’s direction-aware

Acceleration

• Acceleration - is the rate at which velocity changes– Rate means “over time”– Has a direction– Units- distance unit/time unit2

Acceleration formula

a = vf – vi

t

initial velocityfinal velocity

timeacceleration

3 Types of Acceleration

1. Deceleration- – Change in velocity going in a negative direction– Slowing down in a car

2. Zero Acceleration- – A constant velocity in one direction – Like “cruise control” in a car

3. Positive Acceleration– Change in a positive direction– Speeding up in a car

What can affect acceleration?

• Gravity- pulls everything toward the center of the Earth– Causes friction between moving objects

• In a free fall, the speed of objects increases by 9.8m/s for each second it falls

• So gravity constant is 9.8 m/s2

Circular Motion

• Objects moving in a circle still have a velocity • MUST have a constant velocity or would fall inward

or outward• As object moves around circle, direction of

motion is constantly changing (red arrow)– Therefore:• velocity & acceleration

is always changing