 # MECHANICS MECHANICS – The branch of Physics that deals with the motion of objects and the forces that change this motion. Kinematics – The motion part.

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MECHANICS MECHANICS – The branch of Physics that deals with the motion of objects and the forces that change this motion. Kinematics – The motion part of Mechanics. Dynamics – The force part of Mechanics. 1-D MOTION

POSITION – The separation between an object and a reference point. DISTANCE (x) – The length of the path an object took as it moved between positions. SCALAR QUANTITY SCALAR QUANTITY – A measurement with magnitude but no direction. SIZE

DISPLACEMENT (x) – The straight line distance and direction between an object’s starting position and its stopping position. VECTOR QUANTITY VECTOR QUANTITY – A measurement that has magnitude and direction. Represented by bold face variable (text book) or an arrow above the variable. (Notes)

A. What is their final position with respect to Juniors initial position? B. What is Larry’s total displacement? C. What distance did each veggie travel? PRACTICE L J B 25.0 m 8.0 m 12.0 m Larry the Cucumber walks 25.0 m, east to visit Junior. They then walk 8.0m, west to visit Bob. They then all walk 12.0m, east to go to Krispy Kreme. If Larry now travels back home, what is his displacement now?

SPEED – The RATE of distance. SCALAR

VELOCITY – The RATE of displacement. VECTOR

A soldier marches 18 paces, east in 7 seconds, stops for 5 seconds and then marches 12 more paces east in 6 seconds. What is the soldiers speed and velocity for the whole trip? The soldier now moves 25 paces, west. If this takes 10.0 more seconds, what is the soldiers speed and velocity for the whole trip? (From the beginning) The soldier now marches 5 paces, west in 5.0 seconds. What is the soldiers speed and velocity for the whole trip now? (From the beginning)

Instantaneous Speed/Velocity – The speed/velocity at any moment of time. Constant Speed/Velocity – A speed/velocity that is not changing. Average Speed/Velocity – The constant speed/velocity that would need to be maintained to get the same end distance/displacement in the same time.

1V 3V5V7V 9V 11V Bob does the following: 1V/s for 3 seconds, then rests for 3 seconds, then 2 V/s for 3 seconds

1V 3V5V7V 9V 11V Bob does the following: 3V/s for 4 seconds, then rests for 2 seconds, then -2 V/s for 4 seconds

1. A sprinter runs 100.0 m, west, in 9.70 seconds. A. What is the sprinter’s average velocity? B. At this velocity, how long would it take to run 1609 m (1mile)? C. At this velocity how far would the sprinter travel in 1.00 hour?

2. A swimmer dives into a pool and swims 50.0 m, east in 8.00 seconds and then turns around and swims 30.0 m west in 5.00 seconds. A. What is the average speed of the swimmer? B. What is the average velocity of the swimmer? 50.0 m 30.0 m

3. A car travels 100 miles, east in 5.0 hours, then travels 75 miles, west in another 5 hours and then does one more thing that takes 5 more hours. If the car’s average velocity for the whole trip is 25 miles/hour, east, what displacement did the car have in the third part of the trip?

Acceleration – The RATE of velocity change. GALILEO: “when an object gains or loses equal increments of speed during equal increments of time.” t = time required for the velocity change v f = final velocity v i = initial velocity UNITS? m s s 2 VECTOR

Concept Review: 1. What does it mean if an object has a positive acceleration? 2. What does it mean if an object has a negative acceleration? 3. What does it mean if an object has zero acceleration? 4. Is it possible for an object to have zero velocity and a non-zero acceleration? Explain. 5. How are velocity and acceleration related?

Concept Review 2: 1. Describe the motion of an object that has an acceleration of 5 m/s 2, north? 2. Describe the motion of an object that has an acceleration of 2 m/s 2, east and an initial velocity of 10 m/s, west. 3. Describe the motion of an object that has a = 0 m/s 2 ? 4. What would be the velocities each second for the next 10 seconds for an object that has v i = 10 m/s west and a = 3 m/s 2, east? Describe what this motion would look like. 5. How are velocity and acceleration related?

ACCELERATION PRACTICE 1. A sprinter in the 100 m dash is at full speed by the 20.0 m mark. If the velocity of the sprinter is 15.0 m/s, east by the 20.0 m mark, and if it takes 3.2 seconds to get to this mark, what is the acceleration of the sprinter through the first 20.0 meters of the race? (Hint: What is the sprinter’s initial velocity?)

2. A car accelerates at 7.0 m/s 2, North for 8.0 seconds. What is the final velocity of the car if its initial velocity is: a.0.0 m/s? b.10.0 m/s, North? c.7.o m/s, South? For problem #2, what would the answers be if the acceleration was 7.0 m/s 2, South?

3. How long would it take a train to go from a velocity of 6.0 m/s, East, to 123 m/s, East if its acceleration is 2.73 m/s 2, East?

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