Unit 1: Linear Motion Mrs. Jennings Physics

Physics Comp Book UNIT 1: Linear Motion (@top, BIG!) p. 1 Copy GPS listed on the LTA. Circle the verbs; underline the nouns. Page Contents 2 Concept Map: Linear Motion pt. 1 3 linear motion, distance 4 displacement, speed 5 velocity, acceleration 6 Venn Diagram: Scalar vs. Vector 7 Concept Map: Linear Motion pt. 2 8 Lab SUMUPS: * Distance vs. Displacement * Froggy

Let’s do a Frayer model for linear motion: Definition: Drawing: Motion in a straight line linear motion vertical horizontal What it’s NOT: How to remember:

Concept Map: Linear Motion p. 2 when an object moves we observe— which is calculated by called The position changing How quickly the position changes The rate at which the movement changes

When an object moves, we can observe: For your concept map on p.2 of comp book! The position changing Distance: how far it travels is called (in meters) Displacement: how far its position is from the starting point (in meters with a direction) How quickly the position changes Speed: how fast it’s covering distance (or how much distance is covered in an amount of time) Velocity: how fast it’s position is moving and in what direction relative to some other point (like home or a destination The rate at which the movement changes Acceleration: is it speeding up or slowing down

Displacement Isn’t Distance The displacement of an object is not the same as the distance it travels Example: Throw a ball straight up and then catch it at the same point you released it The distance is twice the height The displacement is zero

Distance & Displacement

Distance & Displacement B 4 m 5 m 3 m You walk from A to B to C. What is your distance traveled? What is your displacement from A? A Your distance traveled is 7m Your displacement form A is 5 m

Let’s do Frayers for distance & displacement in your comp book: How to calculate: Definition: How to remember: Don’t confuse this with:

Types of Speed Instantaneous Speed is the speed at any specific instance or moment in time Ex. On a speedometer reading… you are traveling 35 mph (mi/hr) or 50 km/h or 25 m/s Average Speed is the total distance covered divided by total time

How do you calculate average speed? The average speed of an object is defined as the total distance traveled divided by the total time elapsed OR take the average: (initial speed + final speed) 2 Speed is a scalar quantity … why is it not a vector?

Speed, cont Average speed totally ignores any variations in the object’s actual motion during the trip The total distance and the total time are all that is important SI units are m/s

Speed & Velocity Speed is the distance traveled in a certain time. Velocity is the displacement traveled in a certain time. Velocity is speed in a given direction.

Velocity The average velocity of an object is defined as the total displacement traveled divided by the total time elapsed Velocity is a vector quantity

Velocity It takes time for an object to undergo a displacement The average velocity is rate at which the displacement occurs generally use a time interval, so let ti = 0

Velocity, cont. Direction will be the same as the direction of the displacement (time interval is always positive) + or - is sufficient to indicate direction Units of velocity are m/s (SI), cm/s (cgs) or ft/s (US Cust.) Other units may be given in a problem, but generally will need to be converted to these

Speed vs. Velocity Cars on both paths have the same average velocity since they had the same displacement in the same time interval The car on the blue path will have a greater average speed since the distance it traveled is larger

Let’s do Frayers for speed & velocity in your comp book: How to calculate: Definition: Wait for the next slide How to remember: Don’t confuse this with:

Speed vs. Velocity You drive from Yakima to Seattle (140 miles away) You stop in Ellensburg for a 2 hr lunch with a friend. Your total driving time is 2 hours What is the average speed? What is the average velocity? (solve these questions in the Frayers) LIST (3) Equation (2) LABEL w/units (4) Solve

Constant Velocity Constant velocity is constant velocity The instantaneous velocities are always the same All the instantaneous velocities will also equal the average velocity

Velocity Example 1 North North 40º North of East

How fast is the plane moving in respect to the ground? Velocity Example 2 How fast is the plane moving in respect to the ground?

Velocity Example 2 How fast is the plane moving in respect to the ground? Notice the two velocities are occuring in the same LINE (linear motion…)

Velocity Example 3 Is this linear motion? How fast is the plane moving in respect to the ground?

How fast is the plane moving in respect to the ground? Velocity Example 3 How fast is the plane moving in respect to the ground?

How fast is the plane moving in respect to the ground? Velocity Example 3 How fast is the plane moving in respect to the ground?

Concept Map: Linear Motion p. 2 when an object moves we observe— which is calculated by called The position changing distance displacement speed velocity acceleration Adding all the legs of the journey Xfinal –x initial Total distance Total time How quickly the position changes xfinal –x initial time The rate at which the movement changes vfinal –v initial time

Scalar vs. Vector Scalar - magnitude only and units (e.g. volume, mass, time, speed, distance) magnitude means SIZE, units: like meter, mile, etc. Vector – magnitude, units & direction (e.g. weight, velocity, acceleration) in other words: where is this “thing” pointing?

Pictorial Representation An arrow represents a vector Length = magnitude (size) of vector Direction = direction of vector

Pictorial Representation This arrow could represent a vector of magnitude 10 point to the “right” This arrow could represent a vector of magnitude 5 point to the “left”

Get your comp book… Draw an empty Venn Diagram like this on p. 6

Label one side scalar, other vector Place these words in the correct space on the diagram: Magnitude Size Direction Units Distance Displacement Speed velocity Acceleration Mass Weight 12 cm 47 kg (mass) 470 Newtons (weight) 50 meters 50 meters West 25 m/s 25 m/s toward home 25 m/s away from home 10 m/s2 10 m/s2 toward the ground

Acceleration Change in velocity divided by the change in time

Acceleration Great animation showing acceleration: http://www.physicsclassroom.com/mmedia/kinema/acceln.cfm Changing velocity (not constant) means an acceleration is present Acceleration is the rate of change of the velocity (how fast the velocity changes) Units: m/s2 (SI) other examples: cm/s2 ft/s2

Average Acceleration Vector quantity When the sign of the velocity and the acceleration are the same (either positive or negative), then the speed is increasing When the sign of the velocity and the acceleration are in the opposite directions, the speed is decreasing

Relationship Between Velocity & Acceleration Uniform velocity (shown by red arrows maintaining the same size) Acceleration equals zero

Relationship Between Velocity & Acceleration Velocity and acceleration are in the same direction Acceleration is uniform (blue arrows maintain the same length) Velocity is increasing (red arrows are getting longer) Positive velocity and positive acceleration

Relationship Between Velocity & Acceleration Acceleration and velocity are in opposite directions Acceleration is uniform (blue arrows maintain the same length) Velocity is decreasing (red arrows are getting shorter) Velocity is positive and acceleration is negative

Let’s do a Frayer for acceleration in your comp book: How to calculate: Definition: Wait for the next slide How to remember: Don’t confuse this with:

Acceleration Example 1 (solve this problem in the Frayer section…) A car is moving at a speed of 35.8 m/s. If it takes 2.0 s to come to a complete stop, what acceleration would it have? LIST (3) Equation (2) LABEL w/units (4) Solve

Acceleration Example 2 A car is said to go "zero to sixty in six point seven seconds". What is its acceleration in m/s2? LIST (3) Equation (2) LABEL w/units (4) Solve

Acceleration Example 3 The driver from the previous problem can't release his foot from the gas pedal. (The gas pedal is also known as the accelerator. Coincidence? I think not.) How many additional seconds would it take for the driver to reach 80 mph? (assuming the acceleration hasn't changed)? LIST (3) Equation (2) LABEL w/units (4) Solve