Motion

Motion Motion is the change of an object’s position over time Motion is the change of an object’s position over time When we say something has moved, we are describing motion When we say something has moved, we are describing motion When we are describing motion, we are comparing it to a frame of reference When we are describing motion, we are comparing it to a frame of reference

Motion Activity On your graph paper, draw a small picture of yourself getting ready to take a walk in the center at the top. On your graph paper, draw a small picture of yourself getting ready to take a walk in the center at the top. The center is West (Draw a dot) The center is West (Draw a dot) You are going to walk 10 squares to the right to Mario’s for a slice of pizza You are going to walk 10 squares to the right to Mario’s for a slice of pizza How far have you moved from West? How far have you moved from West? How far have you traveled? How far have you traveled?

Motion Activity You forgot your physical science notebook, so you have to run home 14 squares in the other direction and get it You forgot your physical science notebook, so you have to run home 14 squares in the other direction and get it How far have you moved from West? How far have you moved from West? How far (total squares) have you traveled? How far (total squares) have you traveled?

Motion Activity You don’t want to be late for Physical Science, so you run 4 squares back to West You don’t want to be late for Physical Science, so you run 4 squares back to West How far have you moved from West? How far have you moved from West? This is displacement This is displacement How far (total squares) have you traveled? How far (total squares) have you traveled? This is distance This is distance

Distance vs. Displacement Distance – the length of the path traveled between the initial and final positions of something in motion Distance – the length of the path traveled between the initial and final positions of something in motion Displacement – the shortest distance between the initial and final positions of something in motion Displacement – the shortest distance between the initial and final positions of something in motion

Speed When we talk about how fast something is traveling, we are talking about speed When we talk about how fast something is traveling, we are talking about speed Speed is the rate at which an object moves Speed is the rate at which an object moves

Speed How do we calculate speed? How do we calculate speed? Distance VelocityTime

Speed How do we calculate speed? How do we calculate speed? Distance SpeedTime

Speed Distance is usually measured in m or km Distance is usually measured in m or km Time is usually measured in s or hr Time is usually measured in s or hr The unit of speed is usually m/s or km/hr The unit of speed is usually m/s or km/hr Speed is used to describe anything that is changing position: Speed is used to describe anything that is changing position: Runners, cars Runners, cars Ocean currents, winds Ocean currents, winds Moon, Earth Moon, Earth

Constant Speed Some objects have speeds that stay the same as they move Some objects have speeds that stay the same as they move Constant speed Constant speed Speed does not change Speed does not change Plot the distance vs. time for a cheetah traveling 30m/s for 5 seconds Plot the distance vs. time for a cheetah traveling 30m/s for 5 seconds

Constant Speed A cheetah running at constant speed A cheetah running at constant speed Time (s) Distance (m)

Constant Speed

Average Speed Some objects have speeds that change as they move Some objects have speeds that change as they move We have to calculate average speed We have to calculate average speed Speed changes over time Speed changes over time Think about driving in a car Think about driving in a car Speed limit changes Speed limit changes Stop signs and stoplights Stop signs and stoplights

Average Speed Time (s) Distance (m) A car in the pick-up line at West

Average Speed

For things moving at a constant speed, the speed at any point on the line is the average speed For things moving at a constant speed, the speed at any point on the line is the average speed

Instantaneous Speed For things moving at any speed, the speed at a given point in time is the instantaneous speed For things moving at any speed, the speed at a given point in time is the instantaneous speed

Velocity Velocity is a speed in a given direction Velocity is a speed in a given direction If you drive to Raleigh, your average speed could be 97km per hr If you drive to Raleigh, your average speed could be 97km per hr (60miles per hr) Your velocity would be 97 km per hr east Your velocity would be 97 km per hr east You have to include the direction You have to include the direction

Speed and Velocity Practice An airplane flew 1000 km in 4 hr. What is the airplane’s speed? An airplane flew 1000 km in 4 hr. What is the airplane’s speed?

Speed and Velocity Practice A car travels 50 km west in 30 minutes. What is its velocity in km/hr? A car travels 50 km west in 30 minutes. What is its velocity in km/hr?

Speed and Velocity Practice How long will it take a ball to roll 26m if its velocity is 2.0m/s to the right? How long will it take a ball to roll 26m if its velocity is 2.0m/s to the right?

Speed and Velocity Practice If a runner moves with a speed of 1.5m/s and changes her speed to 2.1m/s over 3s, what is her average speed over that 3s? If a runner moves with a speed of 1.5m/s and changes her speed to 2.1m/s over 3s, what is her average speed over that 3s?

Speed and Velocity Practice Work on Velocity Problems Work on Velocity Problems

Acceleration Think about riding a roller coaster Think about riding a roller coaster You go up the first hill at constant speed You go up the first hill at constant speed After the top of the hill, your speed increases quickly After the top of the hill, your speed increases quickly At the bottom of the hill, you slow down and make some turns and keep going At the bottom of the hill, you slow down and make some turns and keep going Rapid changes in velocity Rapid changes in velocity The rate of change in velocity is acceleration The rate of change in velocity is acceleration

Acceleration Something that is speeding up, slowing down, or changing direction is accelerating Something that is speeding up, slowing down, or changing direction is accelerating Acceleration= Final velocity-original velocity Acceleration= Final velocity-original velocityTime What are the units of acceleration? What are the units of acceleration? Acceleration tells you how fast velocity is changing Acceleration tells you how fast velocity is changing

Acceleration Sample Problem: What is the acceleration if we speed up from 10m/s to 30 m/s in 10 seconds? A = V- V A = V f - V i t

Acceleration Sample Problem: A roller coaster car speeds up as it goes down a hill. As it starts down the hill, its speed is 8m/s, and at the bottom of the hill 3 seconds later, its speed is 28m/s. What is its average accleration? A = V- V A = V f - V i t

Gravity Gravity is the acceleration of an object toward Earth Gravity is the acceleration of an object toward Earth g=9.8m/s 2 g=9.8m/s 2

Gravity Example: Brandon drops a water balloon out a window on Dominic, who is standing below. If it takes 10 seconds for the balloon to reach Dominic’s head, what is its speed just before it hits Dominic? g = 9.8m/s 2 - put in place of acceleration g = V- V g = V f - V i What is V i ? t t t t

Momentum Think about a football game Think about a football game A 100kg fullback runs up the field and collides with an 80 kg defensive back. The 100kg fullback gets knocked to the ground by the smaller player. How does that happen? A 100kg fullback runs up the field and collides with an 80 kg defensive back. The 100kg fullback gets knocked to the ground by the smaller player. How does that happen? The defensive back has more momentum The defensive back has more momentum All moving objects have momentum All moving objects have momentum The more momentum a moving object has, the harder it is to stop. The more momentum a moving object has, the harder it is to stop.

Momentum If both players had the same velocity, which player would have more momentum? If both players had the same velocity, which player would have more momentum? What are the units for momentum? What are the units for momentum? p = m x v (p is the abbreviation for momentum) p = m x v (p is the abbreviation for momentum) Momentum has units of kg·m/s Momentum has units of kg·m/s

Momentum Momentum depends on the mass of an object and its velocity Momentum depends on the mass of an object and its velocity Momentum=Mass x Velocity Momentum=Mass x Velocity p=m x v p=m x v In the football game, how can the smaller player knock over the larger player? In the football game, how can the smaller player knock over the larger player? His mass is smaller His mass is smaller His velocity must be larger His velocity must be larger

Momentum What are some things that have a large momentum? What are some things that have a large momentum? Train – has a very large mass Train – has a very large mass Car – large mass, high speed Car – large mass, high speed Harder to stop if moving faster Harder to stop if moving faster Stopping distance is directly related to momentum Stopping distance is directly related to momentum Bullet – small mass, but high velocity Bullet – small mass, but high velocity

Law of Conservation of Momentum When two objects collide, one object transfers momentum to the other When two objects collide, one object transfers momentum to the other The total momentum of a group of objects stays the same unless outside forces act on the objects The total momentum of a group of objects stays the same unless outside forces act on the objects No momentum is lost No momentum is lost Total momentum is the same Total momentum is the same Think about the football players Think about the football players

Law of Conservation of Momentum How do moving objects act? How do moving objects act? Richard_Garriott_Space_Video_Blog_ Conservation_of_Momentum.avi Richard_Garriott_Space_Video_Blog_ Conservation_of_Momentum.avi Richard_Garriott_Space_Video_Blog_ Conservation_of_Momentum.avi Richard_Garriott_Space_Video_Blog_ Conservation_of_Momentum.avi Explains recoil of a gun Explains recoil of a gun mentum/firing_a_gun.htm mentum/firing_a_gun.htm

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