Velocity and Speed Motion Location Reference Point point

Velocity and Speed Motion

Location Reference Point – point at which distance is zero (where you are. . ) Position – separation btn an object and the reference point Example: – What is the position of your friend in reference to your home? What is the position of your love in reference to you? – -7 -6 -5 -4 -3 -2 -1 0 1 2 R. P. (home) 3 4 5 6 7

Distance vs Displacement Distance – space btn two objects – What is the distance btn your friend and your love? Displacement – change in an objects position (Δd) Time – clock reading at an instance – Δt – time btn two readings Example: 2 m 5 m If a person travels all the way around: Distance traveled= 14 m Displacement= 0 m

Vector vs Scalar – quantities that only have a magnitude – Ie distance, time 5 miles, 2 secs, etc. Vector – quantities with a magnitude and direction – Ie position 42 miles North west

Speed S = d/t Average Speed – speed an object had over a distance – Total distance traveled/ total time to get there. Instantaneous Speed – Speed at any given instant of time

Checkpoint What is the speed of a mouse if it travels 15 m in 2. 5 min?

Average Velocity – The average speed of an object in a certain direction (45 mph northwest) V= change in distance/ change in time – Units – meters/second (distance/time) V = Δd/ Δt – Instantaneous velocity An objects velocity at any moment in time – Shown on a speedometer

Examples If Johnny travels a 15 km to school and it takes him 10 min to travel by car, what is his average velocity? – Distance = 15 km – Time = 10 min – Velocity = d/t 15/10 = 1. 5 km/min

Example 2 Johnny is seeing his grandmother today. First, it takes him 10 min to travel 14 km to the drug store to buy her flowers. He stops at the store for 10 min. It then takes him 30 min to get to the nursing home, 45 km away. What is his average velocity on his trip? Trip Portion Distance Time Home to 15 km store 10 min At Store 10 min 0 Store to 45 km 30 min N. H. Remember average velocity = – Total distance/total time Find Total distance – Dtotal = 15 + 0 + 45 = 60 km Find total time – Dtotal = 10 + 30 = 50 min Average Velocity – – – V V V = = = d/t 60/50 1. 2 km/min

Units for Speed or Velocity Distance/time (velocity should also have a direction) Examples – – – m/s miles/hour km/s Converting Units – – All units must be the same throughout an equation 60 s=1 min, 60 min=1 hour, etc

Conversion Example Convert 50 m/s into 50 m km/hour Multiply across the top – 50*60*60*1 1 s – =180000 – – 1*1*1*1000 = 1000 – – 180000/1000 = 180 km/hr Multiply across the bottom Divide top by the bottom 60 s 60 min 1 km 1 min 1 hour 1000 m

Visualizing Motion Graphing Speed/Velocity – Plot time on x axis – Distance on y axis – Slope of line created is the speed

Example

Example A dog chasing a rabbit travels 15 m in 5 sec, then stops to find its trail again for 10 sec. It finds the trail, then travels 20 m in 10 sec following it. Graph the dog’s velocity.

Warm Up How far will Roberta travel if she goes 75 km/hr for 65 min?