Physics and Motion

1. Physics and Motion

2. Physics and Motion • If you want to understand how an object (like a car, ball, person, or rocket) moves, you have to understand three things about what it means "to be moving." • These three terms can apply to any object that moves, and are numbers that scientifically describe just how an object's motion is working.

3. These three things are: 1. Position. This is precisely where an object is located. 2. Speed. This is precisely how fast an object is moving. and...(the most difficult for most people)... 3. Acceleration. This is precisely how fast an object's speed is changing.

4. Precision: • 'Precision' refers to 'the number of significant digits' or the 'number of decimal places' you use when recording the result. • Even if the person making a measurement is as accurate as humanly possible, three things can have influence the result: • limitations imposed by the measuring instrument, • variations in dimensions of the object being measured, • and the conditions under which the measurement is being made. • Note: The point – the result can only be as precise as the circumstances warrant

5. RELATING SPEED TO DISTANCE AND TIME Chapter 9.5

6. 3 TYPES OF SPEED 1) AVERAGE SPEED • Is the total distance divided by the total time for an entire trip. • Think starting and stopping (bathroom breaks) 2) INSTANTANEOUS SPEED • Is the speed of an object at any instant in time. • Think radar gun 3) CONSTANT SPEED • Is when an object remains at the same instantaneous speed over a period of time • Think cruise control

7. Speed (velocity) is a measure of the time required for an object to travel a certain distance. • Often measured in m/s or km/h • Distance is the amount of space between two points or objects. • Units used for distance is cm, m, km • Time is the duration between two events • Units used for time are s, min, hr • Note: We need to measure distance and time in order to determine the speed of an object.

8. Formula for speed (or velocity): V = d (distance) t (time) • Formula for average speed: Vav = Δ d = (d2 – d1 ) Δ t (t2 - t1) (delta - Δ) – Greek Symbol meaning “a change in” d2 is final distance t2 is final time d1 is initial distance t1 is the initial time

9. FORMULA FOR SPEED • V = d2 – d1 • t2 – t1 • v = speed (velocity) – measured in m/s or km/h • d = change in distance – measured in mm, cm, m, km • t = change in time – measured in sec, min, hour, year(a)

10. EXAMPLES • 1) Eiko skates to school, a total distance of 4.5 km. She has to slow down twice to cross busy streets, but her overall journey takes 0.62 hours. What is Eiko’s average speed during the trip? • Solution: Δd = 4.5 km , Δ t = 0.62 h, vav = ? vav = Δ d = 4.5 km = 7.3 km / h Δ t 0.62 h Eiko’s average skating speed is 7.3 km/h.

11. Imagine that you are riding on the CaribooDayliner train and you see a sign that reads 120 km. After seeing several signs like this, you decide to time between two of the signs which are 10 km apart. The elapsed time is recorded at 390.6 s. What is the speed of the train in km/h? • SOLUTION: d = 10 km , t = 390.6 s, v = ? t = 390.6 s = 0.1085 h v = d = 10 km = 92 km/h 3600 s t 0.1085 h The train is traveling at 92 km/h.

12. 3) Same information of 2 but the question asked for m/s instead of km/h. • SOLUTION: d = 10 km, t = 390.6 s , v = ? d = 10 km x 1000 m = 10 000 m v = d = 10000 m = 25.60 m/s 1 km t 390.6 s The train is traveling at 25.60 m/s.

13. 4) Kira is trying to predict the time required to ride her bike to the nearby beach. She knows that the distance is 45 km and from other trips, she can average about 20 km/h. How long will her trip take? • SOLUTION: Δ d = 45 km, vav = 20 km/h, Δ t = ? Rearrange Formula for t. Δ t = Δ d = 45 km = 2.3 h vav 20 km/h Kira should be able t make the trip in 2.3 h.