Describing and Measuring Motion Section 1

Reference Point In order to observe an object in motion you must observe the object in relation to another object that appears to stay in the same place. Common reference points: Earth’s Surface Buildings Trees Mountains

Speed Speed: the distance an object travels in one unit of time Common units: Time- seconds, minutes and hours. Distance- meters, kilometers and centimeters. Formula: Speed = Distance Time SI unit for speed is meters per second (m/s)

Try it out… If you walk for 1.5 hours and travel 7.5 km, what is your speed? S= D T S= 7.5 km 1.5 hrs S= 5 km/h

Average Speed Since objects do not travel at a constant speed the average speed is usually calculated. Formula: Average speed= Total Distance (m) Total Time (s)

Try it out… A car travels 30 km in the first 30 minutes of a trip and 20 km in the second 30 minutes, what is the average speed the car travels? Average speed = total distance total time Average speed = 50km 60min Average speed = .83 km/min

Instantaneous Speed The rate at which an object is moving at a given instant in time.

Velocity Velocity is the speed of an object in a particular direction. The only difference from speed is that velocity includes direction. Which of the following is an example(s) of velocity? a. 25 m/s forward c. 55 m/h south b. 1,500 km/h d. all of the above.

Acceleration Section 2

Acceleration Acceleration is the rate at which velocity changes. Acceleration is not just how much velocity changes. It is also how fast velocity changes.

Acceleration Since velocity involves both speed and direction acceleration refers to: Increasing speed- running to catch a bus, throwing a baseball etc. Decreasing speed- a car coming to a red light. Sometimes this is called deceleration. Changing direction- a car changing lanes or going around a curve. Can a car driving at constant speed be accelerating?

Calculating Acceleration Acceleration= final velocity- initial velocity Time It is expressed in m/s/s or m/s2 Suppose you get on your bicycle and accelerate southward at a rate of 1 m/s/s. This means that every second, your southward velocity increased by 1m/s.

Try it out… A roller coaster rapidly picks up speed as it rolls down a slope. As it starts down the slope its speed is 4 m/s. But 3 seconds later, at the bottom of the slope, its speed is 22 m/s. What is its average acceleration?

Show your work! Acceleration = Final Velocity – Initial Velocity Time Acceleration = 22m/s - 4 m/s 3 sec. Acceleration = 18 m/s Acceleration = 6 m/s2 Acceleration is measured in m/s2 or m/s/s