Speed and Velocity What is speed, velocity and acceleration? How does speed, velocity and acceleration relate to Forces & Motion?

2 How does MOTION relate to POSITION and TIME? Description of MOTION often includes speed and is a change in distance. SPEED then is the rate of change in distance or the “rate of motion.” QUESTION:Do you have to see something move to know that motion has taken place? ANSWER:No – because the only thing needed is to see an object has moved a certain distance.

3 Pretend you are looking at your car's speedometer while you are driving. The reading you get from your speedometer is… This is the speed that you are traveling at that moment. instantaneous speed. Measures of Speed

4 Now, let’s say you are on a highway, a car may travel at the same speed for a long period of time this would be… constant speed. This is the speed that does not vary – cruise control. Measures of Speed - Continued

5 Now, let’s say that you are trying to determine the distance you are going to traveled in a given amount of time by the time – this would be… average speed Katy Houston Speed is the distance traveled per unit of time. Measures of Speed - Continued

6 Distance, Speed and Time is shown in the equation: Calculating Speed s = d t...or shortened: s = Speedd = Distance t = Time speed = distance time

7 GUESSGUESS iven nknown quations needed ubstitute numbers olve and solution Solving Word Problems in Physics When you don’t know, you should GUESS!

A car traveled 110 miles in 2 hours. Example 1:: 8 GUESS Read the problem, draw a picture and write down what is given in the problem. Speed Problems – Calculations GUESS W rite down the unknown variables in the problem. D = 110 miles Speed T = 2 hours GivenUnknownEquations NeededSubstitute including unitsSolution 110 miles 2 hours

9 GUESS W rite down the equation needed to solve the problem. Speed D = 110 miles T = 2 hours GivenUnknownEquations NeededSubstitute including unitsSolution GUESS Substitute the known variables into the equation including the UNITS. S = 55 mi/hr GUESS Solve the equation including the UNITS. Speed Problems – Calculations A car traveled 110 miles in 2 hours. Example 1:: S = D T S = 110 miles 2 hours

10 Do the problems 1-3 on your notes.

A runner’s average speed during the 10 kilometer race was 20km/hr. What was his time? Example 2:: 11 GUESS Read the problem, draw a picture and write down what is given in the problem. Consider this Time Problem GUESS W rite down the unknown variables in the problem. D = 10 km Time S = 20km/hr GivenUnknownEquations NeededSubstitute including unitsSolution 10 km Speed of runner: 20 km/hr

12 GUESS W rite down the equation needed to solve the problem. D = 10 km Time S = 20 km/hr GivenUnknownEquations NeededSubstitute including unitsSolution GUESS Substitute the known variables into the equation including the UNITS. T =.5 hr GUESS Solve the equation including the UNITS. Consider this Time Problem S = D T 20km/hr = 10 km T Example 2:: A runner’s average speed during the 10 kilometer race was 20km/hr. What was his time?

13 Do the problems 4-5 on your notes.

You decide to go to Dallas and visit your family. They tell you it takes 4 hours to get there if you drive 70mph (miles per hour). How many miles is it to their house? Example 3:: 14 GUESS Read the problem, draw a picture and write down what is given in the problem. Consider this Distance Problem GUESS W rite down the unknown variables in the problem. T = 4 hours Distance S = 70mph GivenUnknownEquations NeededSubstitute including unitsSolution ?

15 GUESS W rite down the equation needed to solve the problem. S = 70 mph Distance T = 4 hours GivenUnknownEquations NeededSubstitute including unitsSolution GUESS Substitute the known variables into the equation including the UNITS. D = 280 miles GUESS Solve the equation including the UNITS. Consider this Distance Problem Example 3:: You decide to go to Dallas and visit your family. They tell you it takes 4 hours to get there if you drive 70mph (miles per hour). How many miles is it to their house? S = D T 70 mph = D 4 hours

16 Do problem 6 on your notes.

17 A distance/time graph makes it possible to “see” speed. This graph shows how fast the swimmers went during their workout. Which swimmer swam at a constant (the same) speed throughout her workout? Which one stopped during his/her workout? Constant speed Stopped here 400 meters at 10, 15, & 20 minutes Is a diagonal straight line Graphing Speed

18 Make the speed graph in your notes & answer the questions.

19 Instantaneous speed (Reading on your speedometer) and average speed does not involve direction. So, what would involve both speed and direction…… VELOCITY. Difference between SPEED & VELOCITY

20 55 mi/hr All of these cars had the same SPEED but, different VELOCITIES because they were traveling in different directions. For example – making a right turn with the steering wheel. Velocity has BOTH speed & direction. If you change direction, you have changed your velocity. And if you have changed your speed, you have changed your velocity. Therefore, any change in speed OR direction is a change in velocity! Difference between SPEED & VELOCITY

21 Why do you think it is important to know the VELOCITY of a hurricane? What difference would it make if it were traveling Northwest or Northeast? Challenge Questions

22 Distance, Velocity and Time is shown in the equation: Calculating Velocity V = D T...or shortened: V = Velocity d = Displacementt = Time Velocity = Distance Time

23 You are HERE!!! Houston

Hurricane Maurice is traveling in the Gulf of Mexico towards Galveston Island and the weatherman said it should hit Galveston in 4 hours and is approximately 200 miles offshore. What is Hurricane Maurice’s velocity? Example 4:: 24 GUESS Read the problem, draw a picture and write down what at is given in the problem. Velocity Problems – Calculations GUESS W rite down the unknown variables in the problem. D = 200 miles Velocity T = 4 hours GivenUnknownEquations NeededSubstitute including unitsSolution 200 miles 4 hours

25 GUESS W rite down the equation needed to solve the problem. D = 200 miles Velocity T = 4 hours GivenUnknownEquations NeededSubstitute including unitsSolution GUESS Substitute the known variables into the equation including the UNITS. V = 50 mi/hr Northwest GUESS Solve the equation including the UNITS. Velocity Problems – Calculations V = D T V = 200 miles 4 hours Hurricane Maurice is traveling in the Gulf of Mexico towards Galveston Island and the weatherman said it should hit Galveston in 4 hours and is approximately 200 miles offshore. What is Hurricane Maurice’s velocity? Example 4::

26 Do problems 7 & 8 on your notes.

27 More Information about Velocity Displacement, Velocity and Time If the velocity is NEGATIVE, there is no speed less than zero. So the direction must have changed and it went backwards. If the velocity is POSITIVE, there is speed greater than zero. So the direction must be the same and it went forward.

28 Speed & Velocity – Just for Fun! In your own words, explain the difference between speed and velocity.