fun side of mechanics
DESCRIPTION
Fun Side of Mechanics. By Jonathan Abbott. What Is it?. What is Mechanics? It is the study of Motion. Mass Property of an object: how much stuff is in an object Weight How much gravity pulls on a object Inertia The tendency for an object to resist change in motion Newton’s First Law - PowerPoint PPT PresentationTRANSCRIPT
FUN SIDE OF MECHANICSBy Jonathan Abbott
WHAT IS IT? What is Mechanics?
It is the study of Motion. Mass
Property of an object: how much stuff is in an object Weight
How much gravity pulls on a object Inertia
The tendency for an object to resist change in motion Newton’s First Law
An object in motion stays in that motion until acted upon by an outside force
Newton’s Second Law Force = Mass x Acceleration
WHAT IS IT? Force
A push or a pull Net force
The sum of all the forces on an object Speed
Distance/time Displacement
Vector pointing from start to end Velocity
Displacement/Time: a rate of change in position Acceleration
A rate of change in velocity Scalar vs Vector
Scalar: Only magnitude, Vector: magnitude and direction.
BONUS QUESTIONS What is i-Hat, j-Hat, and k-Hat?
They are unit vectors. Unit vectors have a magnitude of 1 unit and
point in a particular direction. What is Simple harmonic Motion? (What are
two examples I gave last week). Simple Harmonic Motion is when an object
oscillates (like a sine or cosine function) One example is idling on a unicycle Another example is a mass on a spring.
PRACTICE QUESTIONS A car initially traveling at 6 m/s accelerates
at constant acceleration of 3 m/s2 until it reaches the speed limit of 18 m/s (~40 mph). What distance does it travel during this time?
Answer: 48m We can use average velocity to get this answer
too! A soccer ball is kicked at an angle Θ above
the horizontal at velocity v. What will be the range of the soccer ball if it travels over flat ground?
Answer: Δx = v2 /g * sin (2 Θ) So what angle will give the maximum range?
TWO TYPES OF FRICTION: STATIC AND KINETICStatic friction is when two objects
are not scraping with each other (not moving/sliding).
Kinetic friction is when the two objects are scraping with each other (moving/sliding).
IDENTIFY THE TYPE(S) OF FRICTION
Kinetic between Skateboard and Rail
Static between Feet and Skateboard
IDENTIFY THE TYPE(S) OF FRICTION
Static between Wheels and road
www.flickr.com/photos/question_everything/3893946197/.
COEFFICIENT OF FRICTIONThe force of friction is given by:
Ffriction = μ * Nμ is the “coefficient of friction”N is the normal force. (Do you
remember what that was?)
COEFFICIENT OF FRICTION The coefficient of static friction is usually
greater than the coefficient of kinetic friction. Usually the coefficient of friction is less than
1. The coefficient of friction only depends on
the two objects in contact
WHAT IS THE BEST WAY TO MOVE THIS ROCK?
Jerk it so that it starts to move. Then keep it moving
http://www.flickr.com/photos/michaelimage/530418902/
WHY MIGHT WET ROADS BE A PROBLEM? Guess what the coefficient of friction is
between tires and a dry road Answer: about .7
Guess what the coefficient of friction is between tires and a wet road Answer: about .4
Source: http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/frictire.html
WHAT IS THE BEST WAY TO STOP A CAR MOVING ON ICE?
http://www.flickr.com/photos/egazelle/3111507422/sizes/z/in/photostream/
Pump the brakes!
LAB! We are going to test the coefficient of friction
for a whole bunch of objects.
a
bcΘ
3
2
1
IDENTIFY ALL OF THE ACTION-REACTION PAIRS
FREE BODY DIAGRAMS, WITH FRICTION!
CENTER OF MASS The center of mass is where a force (like
gravity) acts on an object. We care about the center of mass because
next week when we discuss balance, the location of the center of mass is very important.
WHERE IS THE CENTER OF MASS?
2m
1m