# Physics 121 Mechanics

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14 Νοε 2013 (πριν από 4 χρόνια και 6 μήνες)

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Physics 121
Mechanics

Course Overview

Dr. Mark C. Waterbury

Lectures by James L. Pazun

1

Models, Measurements and
Vectors

Goals for Chapter 1

To know standards and units and be able to do
unit conversions.

To express measurements and calculated
information with the correct number of
significant figures.

To be able to add vectors.

To be able to break down vectors into
x

and
y

components.

Measurement

Physics is an experimental science.

Observe phenomena in nature.

Make predictions.

Models

Hypothesis

Theories

Laws

Lectures by James L. Pazun

2

Motion Along a

Straight Line

Goals for Chapter 2

Become comfortable with displacement,
velocity, and acceleration.

Explore motions at constant acceleration.

Be able to graph and interpret graphs as they
describe motion.

Be able to reason proportionally.

Examine the special case of freely falling bodies.

Consider relative motion.

Motion

Motion is divided into two areas of study:

Kinematics

This will be our focus in chapter 2.

Kinematics describes the movement of the object.

Dynamics

Will come in Chapter 4 and after.

Why is this object moving?

question.

Lectures by James L. Pazun

3

Motion in a Plane

Goals for Chapter 3

To study position, velocity, and acceleration
vectors.

To frame two
-
dimensional motion as it occurs in
the motion of projectiles.

To restrain two
-
dimensional motion to a circular
path and understand uniform circular motion.

To study the new concept of one motion frame
relative to another.

Velocity in a plane

Vectors in terms of Cartesian
x

and
y

coordinates may
now also be expressed in terms of displacement and
angle.

Lectures by James L. Pazun

4

Newton

s Laws of Motion

Goals for Chapter 4

To understand force

either directly or as the
net force
of multiple components.

To study and apply Newton

s First Law.

To study and apply the concept of mass and
acceleration as components of Newton

s
Second Law.

To differentiate between mass and weight.

To study and apply Newton

s Third Law.

To open a new presentation of problem data in
a free body diagram
.

Dynamics, a new frontier

Stated previously, the onset of physics separates
into two distinct parts:

statics and

dynamics.

So, if something is going to be dynamic, what
causes it to be so?

A force is the cause, it is either

pushing or

pulling.

Types of Force Illustrated I

Figure 4.1

Lectures by James L. Pazun

5

Applications of

Newton

s Laws

Goals for Chapter 5

To study conditions that establish equilibrium.

To study applications of Newton

s Laws as they
apply when the net force is not zero.

To consider contact forces and the effects of
friction.

To study elastic forces (such as spring force).

To consider forces as they subdivide in nature
(strong, electromagnetic, weak, and
gravitational).

Two dimensional equilibrium

Example 5.2

Both
x

and
y

forces must be considered separately.

Follow worked example 5.2 on page 130.

Lectures by James L. Pazun

6

Circular Motion and Gravitation

Goals for Chapter 6

To understand the dynamics of circular motion.

To study the unique application of circular
motion as it applies to Newton

s Law of
Gravitation.

To examine the idea of weight and relate it to
mass and Newton

s Law of Gravitation.

To study the motion of objects in orbit as a
special application of Newton

s Law of
Gravitation.

In section 3.4

We studied the kinematics of circular motion.

Centripetal Acceleration

Changing velocity vector

Uniform Circular Motion

We acquire new terminology.

Period

Frequency

Lectures by James L. Pazun

7

Work and Energy

Goals for Chapter 7

Overview energy.

Study work as defined in physics.

Relate work to kinetic energy.

Consider work done by a variable force.

Study potential energy.

Understand energy conservation.

Include time and the relationship of work to
power.

Introduction

In previous chapters we studied motion

Sometimes force and motion are not enough to solve a
problem.

We introduce
energy
as the next step.

An Overview of Energy

Energy is conserved.

Kinetic Energy describes motion and relates to the mass of
the object and it

s velocity squared.

(some) Energy
on earth originates from the sun.

Energy on earth is stored thermally and chemically.

Chemical energy is released by metabolism.

Energy is stored as potential energy in object height and mass
and also through elastic deformation.

Energy can be dissipated as heat and noise.

Lectures by James L. Pazun

8

Momentum

Goals for Chapter 8

To study momentum.

To understand conservation of momentum.

To study momentum changes during collisions.

To add time and study impulse.

To understand center of mass and how forces act
on the c.o.m.

To apply momentum to rocket propulsion.

Momentum is a vector quantity.

Figure 8.1

Momentum can cause injury ( a concussion)

This is a frame of reference problem just like a passenger in a car. When the brain and skull are
moving at the same velocity, there is no problem. If the skull changes abruptly the brain does
not, there is a possibility of an injury.

Lectures by James L. Pazun

9

Rotational Motion

Goals for Chapter 9

To study angular velocity and angular
acceleration.

To examine rotation with constant angular
acceleration.

To understand the relationship between linear
and angular quantities.

To determine the kinetic energy of rotation and
the moment of inertia.

To study rotation about a moving axis.

Rigid bodies can rotate around a fixed axis.

Figure 9.1

Lectures by James L. Pazun

10

Dynamics of Rotational
Motion

Goals for Chapter 10

To study torque.

To relate angular acceleration and torque.

To examine rotational work and include time to study
rotational power.

To understand angular momentum.

To examine the implications of angular momentum
conservation.

To study how torques add a new variable to
equilibrium.

To see the vector nature of angular quantities.

Definition of torque

Figure 10.1

Torque (

⤠i猠摥晩湥f 慳

The moment arm is the
perpendicular distance
from the point of force
application to the pivot
point.

=
F
l