Unit 2-1: Relative Motion and Speed

Motion is Relative ❖ Although it may not appear as such, everything moves. ❖ Even things that appear to be at rest are moving in relation to the sun and stars. ❖ Relative - with respect to something else.

Regis, this coffee table book is not moving right? That’s right Kramer. But it is moving, Regis How is that true. I can see that the book isn’t moving. The book, like the table it is on, is moving at about 30 kilometers per second relative to the sun. But relative to us, it is not moving, correct? That’s right! Its moving relative to an outside observer. But to us, it is not moving.

Motion is Relative ❖ Examples of relativity: ❖ Ever been sitting at a traffic light and felt like your car was creeping forward? ❖ Is 3AM early or late? ❖ Is there a difference between two cars heading at each other at the following speeds: ❖ One traveling at 5km/h, the other at 15km/h. ❖ One traveling at 20km/h, the other at 0km/h. ❖ One traveling at 10km/h, the other at 10km/h.

Motion is Relative ❖ To be clear, when discussing motion in class, it will be relative to things in our environment. Unless otherwise stated. ❖ Ex: An Indy car racing at 200km/h is moving relative to its track and/or the spectators.

Speed ❖ It’s pretty obvious that a moving object will cover a distance in a given amount of time. ❖ Speed is a measurement of how fast something is moving. ❖ It is the rate at which distance is covered. ❖ Rate: change divided by time. ❖ Speed: Change in distance divided by time.

Speed ❖ Speed is always measured in terms of a unit of distance per a unit of time. ❖ Common units include: ❖ Kilometers per hour (km/h) ❖ Meters per second (m/s) ❖ Kilometers per second (km/s)

Speed ❖ Formula for speed: Distance/Time ❖ Examples: ❖ A car travels 18 kilometers in 2.5 hours. ❖ A jogger runs a 5 kilometer race in 3 hours. Express your answer in terms of meters per second.

Instantaneous Speed ❖ Objects do not always move at the same speed. ❖ Objects can speed up or slow down over the course of travel. ❖ In a car, you can determine your instantaneous speed by looking at your speedometer.

Average Speed ❖ When planning out a trip, most people want to know how long it will take to get there. ❖ We use the average speed to determine how long it will take to cover a distance. ❖ This is because the car is not traveling at the same instantaneous speed the entire trip. ❖ Think about it, it takes time to get to the highweay and time once you get off the highway.

Average Speed ❖ Average speed is calculated by: Total Distance covered divided by time. ❖ Example: ❖ If we travel 120km in 2 hours: ❖ 60km/h ❖ If a car drives for 3 hours at an average speed 25km/h, how far would you travel? ❖ 75km

Practice ❖ Ex 1: ❖ Determine the average speed of a car that covers a distance of 24.5 kilometers over the course of 1.3 hours. Express your answer in terms of meters per second. ❖ Ex 2: ❖ Determine the average speed of a go-cart that travels 1855 meters in 455 minutes. Express your answer in terms of meters per second

Practice ❖ Ex 3: ❖ How long would it take to travel 180km while traveling at 45km/h? ❖ Ex 4: ❖ Determine how much time it would require to travel 400km if you were traveling at 22m/s. Express your answer in minutes.

Practice ❖ Ex 5: ❖ Determine how much distance would be covered if you traveled for 2.3 hours traveling at a distance of 18m/s. Express your answer in terms of kilometers. ❖ Ex 6: ❖ How far can you travel after walking at 9m/s for 45 minutes. Express your answer in meters.