Chapter TwoMotion in One Dimension

2.1 Displacement2.2 Velocity2.3 Acceleration2.4 Motion Diagrams2.5 One-Dimensional Motion with constant acceleration2.6 Freely Falling Objects

Observation What is it?How do we describe it?How does it happen?

Dynamics

• The branch of physics involving the motion of an object and the relationship between that motion and other physics concepts:

• Kinematics is a part of dynamics– In kinematics, you are interested in the description of motion

– Not concerned with the cause of the motion

How do we describe motion?So …..

Remember the Fundamental Quantities for Everything:

Length Mass Time (direction)

Motion should be able to be described with these quantities. HOW?

Quantities in Motion

• Any motion involves hierarchical concepts– Displacement in time– Velocity (change of the above)– Acceleration (change of the above)

• These concepts can be used to study objects in motion

The study of motion in time

The premeditated study of motion by the ancients was focused on the heavenly bodies.

The GREEKS were the first to study the heavens in a systematic and detailed manner. They understood the motion of the heavenly bodies. They created a model that explained the observations: GEOCENTRIC model

Copernicus corrected the understanding of motion: HELIOCENTRIC model

GALILEO really got things going.

Galileo Galilei (1564-1642)

Galileo’s workshopat the

Deutches Museumin

Munich, Germany

Galileo Galilei (1564-1642)

Made astronomical observations with a telescope

Experimental evidence for description of motion

Quantitative study of motion

Acceleration of gravity is independent of the mass of the falling object!

Iron ball

Wood ball

Galileo

Quantities in Motion

–Displacement in time– Velocity (change of the above)– Acceleration (change of the above

Defined as the change in position

Position

• Defined in terms of a frame of reference– A choice of coordinate axes – Defines a starting point for measuring

the motion• Or any other quantity

– One dimensional, so generally the x- or y-axis

In this chapter we are examining 1 dimensional motion

Displacement

• the change in position = –

• f stands for final and i stands for initial

– Units are meters (m) in SI

Δ ≡ −f ix x xΔ ≡ −f ix x x

NOTE: Displacement is DIFFERENT from length

Displacement REQUIRES a coordinate system

Displacement Examples

• From A to B– xi = 30 m– xf = 52 m Δx = 22 m– The displacement is

positive, indicating the motion was in the positive x direction

• From C to F– xi = 38 m– xf = -53 m Δx = -91 m– The displacement is

negative, indicating the motion was in the negative x direction

Displacement, Graphical

Quantities in Motion

– Displacement in time

– Speed & Velocity (change of the above)– Acceleration (change of the above

change in displacement in time

Scalar and Vector Quantities

• Scalar quantities are completely described by magnitude only

• Vector quantities need both magnitude (size) and direction to completely describe them– Generally denoted by boldfaced type and an

arrow over the letter– + or – sign is sufficient for this chapter