Linear Motion

Relative Motion Motion is relative An object’s motion is always described in reference to another object

Relative Motion When an object is said to be traveling at 60 km/h (or at any speed), it is implied that it is moving at 60 km/h relative to the Earth.

Relative Motion CLICK HERE TO WATCH THE VIDEO! Jamiroquai “Virtual Insanity” Travelling Without Moving 1997 Video of the Year

Vectors and Scalars Vector- a quantity possessing both magnitude and direction Scalar- a quantity possessing only magnitude

Vectors and Scalars Examples of Vectors: Displacement (Δx) Velocity (v) Acceleration (a) Force (F) Momentum (p)

Vectors and Scalars Examples of Scalars: Distance (d) Mass (m) Speed (v) Time (t)

Speed Instantaneous speed: the speed that something has at any one instance Average speed: the speed of an object over a time interval

Speed The average speed for a trip might be 53 miles/hour. However, during this trip your instantaneous speed might have been 0 miles/hour at a stoplight... ...or 70 miles/hour on the open road.

What are the units of speed? miles/hour…………….mph kilometer/hour……….km/h meters/second……….m/s furlongs/fortnight?

Speed 1. What is the average speed of a cheetah that sprints 100 meters in 4 seconds? 2. How about if it sprints 50 m in 2 s?

Velocity Velocity = {speed with a direction} Examples: 70 mph is a speed. 70 mph North is a velocity.

What are the units of velocity? Velocity has the same units as speed except they also have a direction

Velocity and speed equations

Velocity vs. speed The speedometer of a car moving to the east reads 100km/h. It passes another car that moves to the west at 100km/h. Do both cars have the same speed? Do they have the same velocity?

Conceptual Review In an unusual move by the New York State Department of Transportation, all of the "speed limit" signs were replaced with "velocity limit" signs. What would such a sign look like? How could one travel faster than the old speed limit without violating the new velocity limit?

Which device(s) on a car can be used to change … its speed? Conceptual Review Which device(s) on a car can be used to change … its speed? its velocity but not its speed?

Conceptual Review A car driving on a circular test track shows a constant speedometer reading of 100 kph for one lap. Describe the car's speed during this time. Describe its velocity. How do the speed and velocity compare?

Conceptual Review Is it possible for an object to have … constant speed and changing velocity, changing speed and constant velocity?

Conceptual Review Why are the devices in cars called speedometers and not velocitometers?

Relative Motion…one more time CLICK HERE TO WATCH THE VIDEO OK Go “Here It Goes Again” Oh No 2007 Grammy award for "Best Short-Form Music Video”

Acceleration Acceleration is the rate of change of velocity.

Acceleration What are the units of acceleration? miles/hour/second…………….mi/h/s kilometer/hour/second……….km/h/s meters/second/second……….m/s/s or m/s2

Acceleration equations

Acceleration Acceleration is the positive or negative depending on the direction of the acceleration.

An object traveling with a constant positive velocity Acceleration An object traveling with a constant positive velocity

An object traveling with a constant negative velocity Acceleration An object traveling with a constant negative velocity

An object traveling with a positive velocity, positive acceleration.

An object traveling with a positive velocity, negative acceleration.

An object traveling with a negative velocity, negative acceleration.

An object traveling with a negative velocity, positive acceleration.

Graphs of Motion On a displacement vs. time graph the slope of the line is equal to the velocity of the object. On a velocity vs. time graph the slope of the line is equal to the acceleration of the object. On a velocity vs. time graph the area underneath the curve is equal to the displacement of the object.