Introduction to Mechanics Mechanics It has nothing to

Introduction to Mechanics

Mechanics • It has nothing to do with the people you call when your car needs to be repaired. • It is the study of motion.

Historical Development of Mechanics Aristotle vs. Galileo

Aristotle He said that we must first understand why objects move.

Aristotle • Things move because they “desire” to do so. • Light things “desire” to rise to the heavens. • Heavy things “desire” to sink to earth. • In short, objects have a natural tendency.

Aristotle Early scientists like Aristotle were called natural philosophers.

Galileo said that we should first study how things move, and then we should describe why they move.

Mechanics the study of motion Dynamics Kinematics Why? cause How? Statics Stationary things react to pushes and pulls.

Mechanics is the study of 1. 2. 3. 4. life. motion. work. systems. Question

T/F Aristotle believed that we should first determine why things move. T Question

System an artificial boundary used to isolate an object or objects

Surroundings everything outside of the system

Systems Scientists are free to select any system as they study the motion of objects. Examples: you, your desk, the floor you and your desk

Frame of Reference • When a car zooms by you, it is moving.

Frame of Reference • But if you are in the car, it seems that the car is standing still and everything else is speeding past the windows.

Frame of Reference What’s the difference? your frame of reference

Frame of Reference What is THE frame of reference? you (How self-centered!) the earth the sun the galaxy

Frame of Reference • There is no “THE frame of reference. ” • Choose the best frame of reference for the problem being solved.

Frame of Reference The frame of reference you choose determines how the motion will be described. Sun North Pole Earth

Kinds of Reference Frames 1. Fixed—the reference frame is stationary, but the system moves. 2. Accelerated—the reference frame accelerates with the system. 3. Rotational—the reference frame accelerates, but the system is stationary.

Coordinate Axis Number Line • Zero is the origin. • Negative numbers are to the left of the origin. • Positive numbers are to the right of the origin.

Time non-physical continuum that orders the sequence of events

Time • sometimes called the spacetime continuum • created by God • Before time was, God is. “I AM. ”

Time • Any event that happens must occur within a span of time. • The start of that time span is called the initial time (ti). • The end of that time span is called the final time (tf).

Time • The difference between the initial and final time is the time interval. • It is called Δt (“delta tee”) and is found by subtracting the initial time from the final time.

What is another name for a coordinate axis? 1. 2. 3. 4. fulcrum space-time continuum number line reference frame Question

Scalar measurement that has a magnitude (amount) with no direction indicated Examples: 13 m 47 km/h

Scalar Since the smallest measurement is zero, scalars never have a negative magnitude. This paper has a measurement of 215. 7 mm.

Vectors measurement that has both a magnitude and a direction Examples: 13 m forward 47 km/h ENE

Vectors The magnitude part of a vector is considered to be a scalar.

Vectors • Vectors are shown force on the coordinate (F) axis by an arrow. • The length indicates the magnitude. • The arrowhead indicates the weight direction. (w)

T/F Scalar measurements have magnitude and direction. F Question