Forces and MotionUnit 19
What words can you think of to describe the motion of an object?
VELOCITYThe word scientists use to describe how fast an object is moving in a certain direction.
Velocity is measured as:a change in distance per change in timechange in distancechange in timeWhat are some things you can think of that are measured like this?
What are some examples of objects that move at high velocities?220 mph1600 mph
Extreme Velocities17,000 mph40,000 mph
What are some examples of lowvelocities?50 yds/hr (.03 mph)1.2 mph
What units would you use to measure the velocity of an object moving in this classroom?meters per secondmsMeters per second tells us how many meters something can move in one second.
Converting Velocities1 highway, 0 city1 hwy, 0 citym/s into km/hrms“What kind of mileage does this get?”1000 m/km3600 seconds/hrJust take the m/s multiply by 1000 and divide by 3600
NSF North Mississippi GK-8
What else can we know about an object’s motion besides velocity?What if the object speeds up?What if the object slows down?What if the object’s velocity changes?
Scientists have a special way to measure a change in velocity:AccelerationAcceleration is a change in velocity.
Visualizing AccelerationHere you can see how the ball travels a further and further distance each second.That is because its velocity is continuing to increase.
If you’re speeding up, you have positive acceleration.If you’re slowing down, you have negative acceleration.
Example:You’re driving along in your car and suddenly have to slam on your brakes for a red light.  Negative or positive acceleration?  High or low acceleration?
AnswersNegative AccelerationHigh Rate
Example:You’re an astronaut waiting in your shuttle for takeoff.  Suddenly the rockets fire and you’re on your way.  High or low positive or negative acceleration?
Or you are a drag racer
Answer High positive acceleration because you’re speeding up quickly.
Example:You’re driving down the highway when your car runs out of gas and you slowly roll to a stop on the side of the road.
Answer Low negative acceleration because you’re slowing down slowly.
Example:You are at cruising speed on the highway. You no longer feel any pressure against the seat or are lurching forward.What is your acceleration?
Answer Zero, because you are at constant velocityThat velocity can be fast, slow, or not moving at all.
Challenge Question:You throw a basketball up in the air.  It rises to a certain height and then falls back to earth.Describe its accelerationHint: There are multiple steps
Answer First, high positive acceleration because it speeds up quickly as it leaves your hand.
Answer Then, as it rises, low negative acceleration, because it begins to slow down slowly because of gravity.
Answer At the top of the arch, it has zero acceleration, because it briefly stops moving upward and has constant velocity.
Answer As it begins to fall again, low positive acceleration, because it speeds up slowly.
Answer Finally, when you catch it, high negative acceleration because it slows down very quickly in your hand.
How Do I Graph the Motion of a Particle?
Car 1 is moving with a velocity of 1 m / secThere is zero acceleration
Car 2 has constant velocity throughout at 1 m /secIts acceleration remains zero
Car 3 has a changing velocity throughout, finishing at 7 m / secAcceleration is 1 m / sec2
Quick ReviewVelocity: speed of motion in a directionAcceleration: change in velocityWhat causes an object’s velocity to change?
If you’re riding your bike and want to speed up, what do you do? If you’re driving a car and 	want to slow down, 	what do you do?
 If you’re playing soccer and 	want to move the ball, 	what do you do?Nothing will change speed unless acted upon by a force.If it’s sitting still, it will keep sitting still.  If it’s moving fast, it will keep moving fast.
Only a force can change the velocity of an object.That force can act to accelerate itNSF North Mississippi GK-8
Only a force can change the velocity of an object.That force can act to decelerate it
Then why do things slow down?Flying balls slow down and eventually stop because of the force of gravity.Cars and bikes eventually slow down and stop because of the force of friction.
Then why do things slow down?In space with no friction and no gravity, objects will keep going at the same speed forever without a force to slow them down or speed them up.

Unit 19 - Forces And Motion

  • 1.
  • 2.
    What words canyou think of to describe the motion of an object?
  • 3.
    VELOCITYThe word scientistsuse to describe how fast an object is moving in a certain direction.
  • 4.
    Velocity is measuredas:a change in distance per change in timechange in distancechange in timeWhat are some things you can think of that are measured like this?
  • 5.
    What are someexamples of objects that move at high velocities?220 mph1600 mph
  • 6.
  • 7.
    What are someexamples of lowvelocities?50 yds/hr (.03 mph)1.2 mph
  • 8.
    What units wouldyou use to measure the velocity of an object moving in this classroom?meters per secondmsMeters per second tells us how many meters something can move in one second.
  • 9.
    Converting Velocities1 highway,0 city1 hwy, 0 citym/s into km/hrms“What kind of mileage does this get?”1000 m/km3600 seconds/hrJust take the m/s multiply by 1000 and divide by 3600
  • 10.
  • 11.
    What else canwe know about an object’s motion besides velocity?What if the object speeds up?What if the object slows down?What if the object’s velocity changes?
  • 12.
    Scientists have aspecial way to measure a change in velocity:AccelerationAcceleration is a change in velocity.
  • 13.
    Visualizing AccelerationHere youcan see how the ball travels a further and further distance each second.That is because its velocity is continuing to increase.
  • 14.
    If you’re speedingup, you have positive acceleration.If you’re slowing down, you have negative acceleration.
  • 15.
    Example:You’re driving alongin your car and suddenly have to slam on your brakes for a red light. Negative or positive acceleration? High or low acceleration?
  • 16.
  • 17.
    Example:You’re an astronautwaiting in your shuttle for takeoff. Suddenly the rockets fire and you’re on your way. High or low positive or negative acceleration?
  • 18.
    Or you area drag racer
  • 19.
    Answer High positiveacceleration because you’re speeding up quickly.
  • 20.
    Example:You’re driving downthe highway when your car runs out of gas and you slowly roll to a stop on the side of the road.
  • 21.
    Answer Low negativeacceleration because you’re slowing down slowly.
  • 22.
    Example:You are atcruising speed on the highway. You no longer feel any pressure against the seat or are lurching forward.What is your acceleration?
  • 23.
    Answer Zero, becauseyou are at constant velocityThat velocity can be fast, slow, or not moving at all.
  • 24.
    Challenge Question:You throwa basketball up in the air. It rises to a certain height and then falls back to earth.Describe its accelerationHint: There are multiple steps
  • 25.
    Answer First, highpositive acceleration because it speeds up quickly as it leaves your hand.
  • 26.
    Answer Then, asit rises, low negative acceleration, because it begins to slow down slowly because of gravity.
  • 27.
    Answer At thetop of the arch, it has zero acceleration, because it briefly stops moving upward and has constant velocity.
  • 28.
    Answer As itbegins to fall again, low positive acceleration, because it speeds up slowly.
  • 29.
    Answer Finally, whenyou catch it, high negative acceleration because it slows down very quickly in your hand.
  • 30.
    How Do IGraph the Motion of a Particle?
  • 31.
    Car 1 ismoving with a velocity of 1 m / secThere is zero acceleration
  • 32.
    Car 2 hasconstant velocity throughout at 1 m /secIts acceleration remains zero
  • 33.
    Car 3 hasa changing velocity throughout, finishing at 7 m / secAcceleration is 1 m / sec2
  • 34.
    Quick ReviewVelocity: speedof motion in a directionAcceleration: change in velocityWhat causes an object’s velocity to change?
  • 35.
    If you’re ridingyour bike and want to speed up, what do you do? If you’re driving a car and want to slow down, what do you do?
  • 36.
    If you’replaying soccer and want to move the ball, what do you do?Nothing will change speed unless acted upon by a force.If it’s sitting still, it will keep sitting still. If it’s moving fast, it will keep moving fast.
  • 37.
    Only a forcecan change the velocity of an object.That force can act to accelerate itNSF North Mississippi GK-8
  • 38.
    Only a forcecan change the velocity of an object.That force can act to decelerate it
  • 39.
    Then why dothings slow down?Flying balls slow down and eventually stop because of the force of gravity.Cars and bikes eventually slow down and stop because of the force of friction.
  • 40.
    Then why dothings slow down?In space with no friction and no gravity, objects will keep going at the same speed forever without a force to slow them down or speed them up.