Chapter 10 Motion Notes

Definition of position An object’s location

Definition of Reference Point A location to which another location is compared

Definition of motion A change of position over time.

Ch An Object in Motion Changes Position I. Position describes the location of an object A. Describing a position 1. A reference point is a location to which you compare other locations 2. Longitude and latitude help make it easy to compare locations

reference point motion position An object in motion changes position. SECTION OUTLINE SECTION OUTLINE Position is measured from a reference point. Motion is measured relative to an observer. starting position ending position 10.1 CHAPTER RESOURCES CHAPTER RESOURCES

Measuring Motion Speed is the distance an object travels in a certain amount of time Speed = distance divided by time S = d/t d = s(t) t = d/s Velocity is both speed and direction (v = d/t) Speed and velocity are often interchanged but velocity involves direction

II. Motion is a change in position 6. What provides evidence that motion has happened? A change in position

B. Relative Motion 8. If you are seated on the train, who or what would be moving compared with you? The person outside, the suitcase, and the ground would be moving Who would be still compared to you? The people inside would be still.

B. Relative Motion 9. If you are standing outside the train, who or what would be moving compared with you The people in the train and the train would be moving Who or what would be still? The ground and the suitcase would be still.

10. Summarize the meaning of relative motion. Relative motion is the concept that the motion an observer sees depends on the observer’s frame of reference. Observers in different reference frames see different motions for the same object.

Section 10.2 Speed measures how fast position changes

Definition of speed A measure of how fast something moves through a particular distance over a definite time period.

Definition of velocity A speed in a specific direction.

Definition of Vector A quantity that has both size and direction.

Speed is how fast positions change with time. velocity vector speed Speed measures how fast position changes. SECTION OUTLINE SECTION OUTLINE distance 00:00 00:02 Speed = distance time 10.2 CHAPTER RESOURCES CHAPTER RESOURCES

Speed is how fast positions change with time. SECTION OUTLINE SECTION OUTLINE Velocity is speed in a specific direction. Velocity velocity vector speed Speed measures how fast position changes CHAPTER RESOURCES CHAPTER RESOURCES

A.Calculating Speed I. Position can change at different rates. –A. Calculating speed Requires both distance and time Formula is S = d/t –a. S stands for speed Units: km/h m/h m/s –b. D stands for distance Units: meters(m) kilometers (km), miles (mi) –C. T stands for time Units: seconds (s), hours (h), minutes(min)

3. How does the unit for speed (m/s) relate to the formula for speed? The unit for speed shows a distance unit, the meter, divided by a time unit, the second, as does the formula

Steps for Solving Problems What do you know? What do you want to find out? Write the formula Substitute into the formula Calculate and Simplify Check that your units agree Answer – Circle your answer

B. Average Speed 4.If someone ran 100 meters in 20 seconds, what is her speed? D = 100 m T = 20 s S = ? S = d/t S = 100m/20s S = 5 m/s

B. Average Speed 4.If someone ran 100 meters in 20 seconds, then ran another 100 meters in 25 seconds, what would the runner’s average speed be over the whole 200 meters? D = 200m T = = 45 s S =? S = d/t S = 200 m/45s S = 4.4 m/s

Constant and Average Speed Constant speed means equal distances in equal amounts of time. –Represented by a straight line on a graph Average Speed = total distance divided by total time.

C. Distance-Time Graphs 5. The distance-time graph below shows the motion of a cat. During the 100 seconds shown, the cat was walking, running, and resting. Label each line segment of the graph with a description of the cat’s motion. Explain your answer seconds – walking, cat is moving slowly; seconds – resting, cat is not moving; seconds – running, cat is moving quickly

II. Velocity includes speed and direction. Velocity –Need to know speed and direction –Changing either speed or direction causes a change in velocity –Is considered a vector because it has both size and direction –Represented graphically by an arrow

A-B. Velocity, Velocity versus Speed 7. Explain why velocity is a vector but speed is not. –A vector is a quantity that has both size and direction. Velocity is a vector because it is a measure of both speed, which has a size, and direction. Speed is only a measure of a size, so it is not a vector.

Centripetal Acceleration An object moving in a circle or curve is constantly changing direction therefore it is accelerating (centripetal acceleration) Centripetal acceleration is always towards the center of a circle.

Energy and Change Energy is the ability to do work Two Types of Energy –Potential (PE)– stored energy Associated with the position of an object –Kinetic (KE) – energy of motion Depends on an objects mass & speed.

Gravitational PE Gravitational Potential energy is abbreviated: GPE It depends on an object’s weight and the distance it falls before stopping completely

Law of Conservation of Energy The Law of Conservation of Energy states that energy cannot be created or destroyed. The total amount of energy always remains the same, but it can change form Example: –At the top of the hill the rock as Potential Energy –As it falls the rock loses potential energy and gains kinetic energy

Section 10.3 Acceleration measures how fast velocity changes.

Acceleration Acceleration is the rate at which velocity changes over time. It is a change in velocity resulting from speeding up, slowing down, or changing direction Acceleration = change in velocity divided by time Formula: a = (vf – vi)/t –Vf = final velocity (ending speed) –Vi = initial velocity (starting speed) –t = time (amount of time it takes to start/stop) seconds(s), hours (h), minutes (min)

Acceleration (Cont.) Negative acceleration (deceleration) is a decrease in velocity over time. (slowing down) Any change in velocity is acceleration even if the speed remains the same.

Acceleration in the Same Direction as Motion Acceleration measures how fast velocity changes. acceleration SECTION OUTLINE SECTION OUTLINE Acceleration in the Opposite Direction of Motion Acceleration at a Right Angle to Motion 10.3 CHAPTER RESOURCES CHAPTER RESOURCES

A. Calculating Acceleration 4.What is the formula for acceleration? acceleration = final velocity – initial velocity time What units are used for each of the values? Unit for time = seconds (s) Unit for velocity = m/s Unit for acceleration = m/s 2

A. Calculating Acceleration 5.A skater begins skating at a velocity of 1 m/s. After 4 seconds, her velocity is 3m/s. What is the skater’s acceleration? Show your work. Vi = 1 m/s Vf = 3 m/s T = 4s A = ? a = vfinal – v initial ;a = 3 m/s – 1 m/s; a = 0.5 m/s 2 time 4s

B. Acceleration over Time 6.A car has an acceleration of 4 m/s 2. What will the increase in its velocity be after 2 seconds? If it started with a velocity of 30 m/s, what is its final velocity? A = 4 m/s 2 T = 2 s Vi = 30 m/s A = vf – vi/t 4m/s 2 = vf – 30/2 4(2) = (vf – 30) = 8 m/s; vf = = 38 m/s

C. Velocity-Time Graphs 7. Fill in the velocity- time graph to show the velocity of a ball rolling at a constant speed of 7 m/s for 5 seconds.