1. Introduction to Mechanics

2. An Overview of Mechanics Mechanics is the study of motion Kinematics is a subtopic of mechanics dealing with the description of motion without regard to outside influences Dynamics is another subtopic of mechanics that deals with the forces behind the motion Sometimes, we say that kinematics is the “how” and dynamics is the “why”. Mechanics is the study of motion Kinematics is a subtopic of mechanics dealing with the description of motion without regard to outside influences Dynamics is another subtopic of mechanics that deals with the forces behind the motion Sometimes, we say that kinematics is the “how” and dynamics is the “why”.

3. Vectors and Scalars A scalar is a measurement that has magnitude (number value) only A vector is a measurement that has magnitude and direction Speed is a scalar; velocity is a vector http://www.physicsclassroom.com/Class /1DKin/U1L1b.html http://www.physicsclassroom.com/Class /1DKin/U1L1b.html Try the sample questions at this site to determine whether a quantity is a vector or a scalar A scalar is a measurement that has magnitude (number value) only A vector is a measurement that has magnitude and direction Speed is a scalar; velocity is a vector http://www.physicsclassroom.com/Class /1DKin/U1L1b.html http://www.physicsclassroom.com/Class /1DKin/U1L1b.html Try the sample questions at this site to determine whether a quantity is a vector or a scalar

4. Distance vs. Displacement Distance is the total ground covered on a journey no matter what route is taken If you have to take the long way around a traffic jam, your distance increases Displacement is the straight line drawn from the beginning to the end of a journey, regardless of the path taken The following website has some questions to answer at the bottom of the page http://www.physicsclassroom.com/Class/1DKi n/U1L1c.html http://www.physicsclassroom.com/Class/1DKi n/U1L1c.html Distance is the total ground covered on a journey no matter what route is taken If you have to take the long way around a traffic jam, your distance increases Displacement is the straight line drawn from the beginning to the end of a journey, regardless of the path taken The following website has some questions to answer at the bottom of the page http://www.physicsclassroom.com/Class/1DKi n/U1L1c.html http://www.physicsclassroom.com/Class/1DKi n/U1L1c.html

5. Speed vs. Velocity Average Speed = distance/time = x/t Since distance is a scalar, speed is also a scalar; for example 60mph is a speed Average Velocity = displacement/time = x/t Since displacement is a vector (has direction), velocity is also a vector; for example 60 mph NE Try this website for some examples of speed and velocity http://www.physicsclassroom.com/Class/1DKi n/U1L1d.html http://www.physicsclassroom.com/Class/1DKi n/U1L1d.html Average Speed = distance/time = x/t Since distance is a scalar, speed is also a scalar; for example 60mph is a speed Average Velocity = displacement/time = x/t Since displacement is a vector (has direction), velocity is also a vector; for example 60 mph NE Try this website for some examples of speed and velocity http://www.physicsclassroom.com/Class/1DKi n/U1L1d.html http://www.physicsclassroom.com/Class/1DKi n/U1L1d.html

6. More Velocity Situations If the runner goes around a circular track 1 1/2 times, what is his displacement? Did you guess that it is the diameter of the track? What is the distance covered? Did you guess that it is 1 1/2 times the circumference of the circle? If the runner goes around a circular track 1 1/2 times, what is his displacement? Did you guess that it is the diameter of the track? What is the distance covered? Did you guess that it is 1 1/2 times the circumference of the circle?

7. Circular Motion and Displacement If a runner runs one lap in a certain amount of time, we can calculate his speed as distance/time But, his velocity is zero…why? His displacement is zero because he ended where he started. If a runner runs one lap in a certain amount of time, we can calculate his speed as distance/time But, his velocity is zero…why? His displacement is zero because he ended where he started.

8. Units For Speed and Velocity In science, we use the metric system and distance and displacement are measured in meters Time is measured in seconds no matter what measurement system you are using Therefore, speed and velocity are both measured in meters/second (m/s) In science, we use the metric system and distance and displacement are measured in meters Time is measured in seconds no matter what measurement system you are using Therefore, speed and velocity are both measured in meters/second (m/s)

9. Try these Speed/Velocity Problems #1 and #2 A car travels 1000 m in 50 s. What is the car’s speed? Speed = distance/time = 1000 m/50 s = 20 m/s A car travels 1000 m north in 50 s. What is the car’s velocity? Velocity = displacement/time = 1000 m/50 s = 20 m/s, north A car travels 1000 m in 50 s. What is the car’s speed? Speed = distance/time = 1000 m/50 s = 20 m/s A car travels 1000 m north in 50 s. What is the car’s velocity? Velocity = displacement/time = 1000 m/50 s = 20 m/s, north

10. Sample Problem #3 A car travels 500 m east, 1000 m west and then 2000 m east again. It does this in a time of 100 seconds. What is the car’s average speed? Speed= distance/time = 3500 m/100 s = 35 m/s What is the car’s average velocity? Velocity = displacement/time = 1500 m east/100 seconds = 15 m/s, east A car travels 500 m east, 1000 m west and then 2000 m east again. It does this in a time of 100 seconds. What is the car’s average speed? Speed= distance/time = 3500 m/100 s = 35 m/s What is the car’s average velocity? Velocity = displacement/time = 1500 m east/100 seconds = 15 m/s, east