Honors Physics Semester 1 Review PowerPoint

Distance vs Displacement

0 1 2 3 4 5 6 7 8 9

Distance = magnitude only = 8m

Displacement = magnitude and direction = Δx = x2 – x1

Δx = x2 – x1 = 9m – 1m = +8m

Acceleration

• When you increase your speed in a car, are you accelerating?

• When you turn in a car, are you accelerating?• When you slow down in a car, are you

accelerating?• This is called deceleration or negative

acceleration or acceleration in the direction opposite of the car’s movement.

• Objectives: define distance and calculate speed, and explain what is meant by scalar quantity.

Scalar Quantity:• Quantity with only a numerical value• Distance tells us how far but not in

what direction.• Time• Mass• Temperature

Graphical Analysis

Zero acceleration Positive acceleration

KinematicsSpeed: the rate at which distance is traveled

Constant Speed: speed of object does not change

Average speed = total distance/total time

Units: meters m second s

REVIEW:• Motion: change of position• Scalar: numbers only• Vector: direction• Velocity: change of speed in a given

direction• Acceleration: a change in velocity

• Therefore, a change in speed or a change in direction

Graphs• Position v Time graphs

constant velocity Δv = acceleration

Speed and Velocity• There are two types of Velocity:• 1. Average Velocity V = ∆d/∆tFor example, when a car moved 50 km in 2

hours, the average velocity is 25km/h.• 2. Instantaneous VelocityFor example, when the speed cameras give

you a ticket, they show the car driving at 90 km/h for that instant.

Velocity

What is the velocity of this object between 0-4 sec?

What is the initial starting position of the object?What is the displacement of this object from 3-4

seconds?What is the object’s final position?

Positi

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Graphs• Assuming

the objects motion does not change, what would its position be at t=20s?

Time (seconds)

Positi

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• What is happening to the velocity of these two objects?

• What is happening at t=2s?• At t=4s, which object has greater

speed?

Graphical Analysis

Zero acceleration Positive acceleration

Newton’s First Law of Motion or Law of Inertia: in the absence of an unbalanced force, a body

at rest remains at rest, and a body in motion

remains in motion with a constant velocity

(speed and direction).

Inertia and Newton’s 1st Law

• Inertia - tendency of an object to overcome a change in motion

• Characteristics: more mass = more inertia

Mass is the quantitative measure of inertia.

Net Forces

Normal Force

When an object is sitting on a level surface then the normal force is always equal and opposite of the weight of the object.  

Forces Symbols

Fapp – applied force (push or pull)Fg – force of gravity (always toward center of earth or down)Fn – normal force (always perpendicular to surface)Ff – force of friction (same as surface)

Balanced forces do not change the object’s motion.

FORCES

• Unbalanced forces result in a change in the object’s motion.

Newton’s First Law of Motion or Law of Inertia: in the absence of an unbalanced force, a body

at rest remains at rest, and a body in motion remains in motion with a constant velocity (speed and direction).

Newton’s 3rd Law of Motion

• For every force (action), there is an equal and opposite force (reaction).

Free Fall – Force of Gravity ONLY

• Free Fall: A Particular Acceleration

• How fast a falling object moves is entirely DIFFERENT from how far it moves.

• We will treat x and y separately

• SI Unit: Newton = kg • m/s2

• Force is a vector (magnitude/direction)

Like velocity and acceleration, force has a strength AND a direction

FORCEResultant Force: the total of all forces

acting on an object.

• Force 1 pushes upward with 2 N• Force 2 pushes horizontally with 5 N

Net Forces with angles

Net Forces with angles

What is the net force on this object?

What is Fs?What is FN?

Pull Force of20 N at 16°

50kg

Types of FrictionStatic Friction: Frictional force is sufficient to prevent

motion between surfaces.

Static Friction Formula fs ≤ µsN (static conditions = no movement)

µscoefficient of static friction

Friction (think about ice)

Normal Force

• Normal means perpendicular.• Force that a surface exerts on an object.

Normal Force

• When an object is sitting on a level surface then the normal force is always equal and opposite of the weight of the object.  

Force Formula• Acceleration of an object is

directly proportional to the net force and inversely proportional to its mass.

Acceleration = Force Mass

Momentum and Impulse• The concept of impulse and momentum using

Newton’s 2nd Law: • F = ma a = vf – vi = Δv F = m Δv

t t t• Take t to the other side:

• Impulse-Momentum Theorum = F t = m Δv

• F(t) is called IMPULSE. • It is defined as a force acting through time.• Impulse is numerically equal to the Δ of momentum. • So a force acting for time on some object gives rise to

a change of the object’s momentum.

Is momentum conserved?• YES.• The momentum lost by one object is

gained by the other object.• The total amount is constant.

Elastic Collisions

Total Kinetic Energy is conserved• Follows the Law of Conservation of

Momentum

• Kafter = Kbefore

Inelastic Collisions

Kinetic energy is NOT conserved

• Change in original shapes• Sound and friction – KE lost

Linear Momentum

• Formula: ρ = m v• ρ = momentum• m = mass• v = velocitySI Units?kg m/s

Law of Conservation of Linear Momentum:"the total momentum of an isolated system of interacting bodies remains constant."

OR

"Total momentum of an isolated system before collision is always equal to total momentum after collision.“

Correlates to Newton’s 1st Law of Motion

Radians Correct SI unit for angular measurements

radius to arc length = radian (The Rad)

1 rad = 360˚/2π = 57.3˚

Calculators: switch to rad when told

Period and FrequencyFrequency: number of cycles

per unit of time. f = 1/t or s-1

Period: (t) time it takes an object in circular motion to complete one revolution or cycle

t = 1/fFrequency and period =

inverse relationshipFrequency SI: 1/s = Hertz (Hz)

Heinrich Rudolf Hertz

Uniform Circular Motion Needs 3 things 1. Centripetal Force

Uniform Circular Motion 2. Angular Acceleration 3. Constant Speed

V=Tangential velocitywants to go in a straight line

Gravitational Field Lines for Two Objects

Kepler’s 3rd Law of Planetary Motion

This Law lets us determine a newly discovered planet’s distance from the Sun.

Kepler’s Laws of Planetary Motion

Kepler’s 2nd Law: (Law of Areas)A line from the Sun to a planet sweeps out

equal areas in equal lengths of time.

Escape VelocityWhat kind of energy must a man-made

satellite have to escape Earth’s gravitational pull?

Formula for Escape Velocity:

Escape speed = escape surface of Earth is about 11km/s or 7mi/s

Centrifugal is just Inertia – what Law? Newton’s 1st: an object in motion wants to stay in

that motion and not change speed or direction unless acted upon by an outside force.