Chapter 2 Motion

Think About It! How would you describe speed? How would you describe speed? What would you need to know to figure out speed? What would you need to know to figure out speed? Do you need to see something move to know that motion has occurred? Do you need to see something move to know that motion has occurred?

Motion and Position A reference point is needed to determine position A reference point is needed to determine position Motion: occurs when an object changes position relative to a reference point Motion: occurs when an object changes position relative to a reference point You are moving in your chair You are moving in your chair Relative to the other planets! Relative to the other planets! Earth travels 942 billion meters/ year. How fast is it traveling in mi/hr? Earth travels 942 billion meters/ year. How fast is it traveling in mi/hr?

Distance and Displacement Distance: how far an object has moved Distance: how far an object has moved km, m, cm, etc. km, m, cm, etc. Displacement: distance AND direction of object from starting point Displacement: distance AND direction of object from starting point

Distance and Displacement

Speed Speed: distance traveled in a certain amount of time Speed: distance traveled in a certain amount of time

Constant vs. Changing Speed If speed is constant – can calculate speed over any distance – it’ll be the same! If speed is constant – can calculate speed over any distance – it’ll be the same! Usually speed is changing Usually speed is changing

Average Speed Calculate total distance by total time Calculate total distance by total time

Instantaneous Speed Def: speed at a given point in time. Def: speed at a given point in time. Speedometers show inst. speed Speedometers show inst. speed Constant speed = inst. speed does not change Constant speed = inst. speed does not change

Practice Problems Runner travels 200m dash in 22 s. What is the average speed? Runner travels 200m dash in 22 s. What is the average speed? You had an average speed of 70 mi/hr from the St. Leon exit to the Harrison exit on I-74. It took you 10 minutes to get there. How many miles did you travel? You had an average speed of 70 mi/hr from the St. Leon exit to the Harrison exit on I-74. It took you 10 minutes to get there. How many miles did you travel? You traveled 75 miles at 70 mi/hr from here to Indianapolis. How long did it take you in minutes? You traveled 75 miles at 70 mi/hr from here to Indianapolis. How long did it take you in minutes?

Velocity Def: speed of object AND direction Def: speed of object AND direction speed : velocity as distance : displacement speed : velocity as distance : displacement Velocity can change even if speed is constant Velocity can change even if speed is constant

Moving Continents

Graphing Time on X-AXIS Time on X-AXIS Distance on Y-AXIS Distance on Y-AXIS Constant speed = straight line Constant speed = straight line

Graphing Slope = change in y = rise = distance = speed Slope = change in y = rise = distance = speed change in x run time change in x run time Horizontal line = object at rest Horizontal line = object at rest

Acceleration Section 2

Acceleration Def: rate of change of velocity Def: rate of change of velocity Could be change in speed, direction or both Could be change in speed, direction or both Speeding up  + acceleration Speeding up  + acceleration Slowing down  -- acceleration Slowing down  -- acceleration Speed is changing = acceleration Speed is changing = acceleration

Acceleration + acc. = going in same direction as velocity + acc. = going in same direction as velocity -- acc. = going in opposite direction as velocity -- acc. = going in opposite direction as velocity

Acceleration Changing direction is changing velocity and acceleration Changing direction is changing velocity and acceleration Speed is constant Speed is constant

Calculations If direction doesn’t change velocity = speed If direction doesn’t change velocity = speed Units: m/s 2 Units: m/s 2

Positive Acceleration Jet airliner starts at rest and reaches a speed of 80m/s in 20s. Calculate the acceleration. Jet airliner starts at rest and reaches a speed of 80m/s in 20s. Calculate the acceleration. Has positive slope on graph Has positive slope on graph

Negative Acceleration Skateboarder comes to rest in 2s after a speed of 3 m/s. What is his acceleration? Skateboarder comes to rest in 2s after a speed of 3 m/s. What is his acceleration? Has negative slope on graph Has negative slope on graph

Time Calculations A car had a negative acceleration of 4 m/s 2 when it stopped after having a rate of 40 m/s. How long did it take for the car to stop? A car had a negative acceleration of 4 m/s 2 when it stopped after having a rate of 40 m/s. How long did it take for the car to stop?

Final Velocity Calculations If a vehicle has an initial velocity of 35 m/s accelerates at 20 m/s 2 for 5 seconds, what is it’s final velocity? If a vehicle has an initial velocity of 35 m/s accelerates at 20 m/s 2 for 5 seconds, what is it’s final velocity?

Motion and Forces Section 3

What is force? Def: a push or pull Def: a push or pull Kicking a ball, throwing a ball, etc. Kicking a ball, throwing a ball, etc. Chair has a force on you, atmosphere’s force, etc. Chair has a force on you, atmosphere’s force, etc.

Changing Motion Force causes motion to change Force causes motion to change

Balanced Forces Net Force: combination of two or more forces act on an object at same time. Net Force: combination of two or more forces act on an object at same time. Balanced Forces: forces equal in size but in opposite direction Balanced Forces: forces equal in size but in opposite direction Net force = 0 Net force = 0

Unbalanced Forces Unequal opposite forces - net force will be the difference between the two and move in direction of bigger force Unequal opposite forces - net force will be the difference between the two and move in direction of bigger force

Same Direction Forces Net force is sum of the two and moves in that direction Net force is sum of the two and moves in that direction

Inertia and Mass Inertia: tendency to resist any change in motion Inertia: tendency to resist any change in motion Stop a bowling ball vs. ping pong ball Stop a bowling ball vs. ping pong ball Greater mass of object  greater inertia Greater mass of object  greater inertia Newton’s 1 st Law of Motion Newton’s 1 st Law of Motion

Newton’s 1 st Law of Motion Sir Isaac Newton ( ) Sir Isaac Newton ( ) Def: Object moving at constant velocity keeps moving at that velocity unless an unbalanced net for acts Def: Object moving at constant velocity keeps moving at that velocity unless an unbalanced net for acts Sometimes called “Law of Inertia” Sometimes called “Law of Inertia”

Car Collisons Seat belt vs. No seat belt Seat belt vs. No seat belt Speed of 50 km/hr collides with wall Speed of 50 km/hr collides with wall Car stops in.1s Car stops in.1s No belt = person keeps moving at 50 km/hr No belt = person keeps moving at 50 km/hr Seat belt = slows person to stop (air bags help too) Seat belt = slows person to stop (air bags help too)