Motion So Far Distance vs Displacement Speed vs

  • Slides: 23
Download presentation
Motion So Far…. • • • Distance vs. Displacement Speed vs. Velocity Average Speed

Motion So Far…. • • • Distance vs. Displacement Speed vs. Velocity Average Speed Average Velocity Acceleration – “Speeding Up” – “Slowing Down” Dr. Joseph W. Howard ©Spring 2008

Why do objects move? Dr. Joseph W. Howard ©Spring 2008

Why do objects move? Dr. Joseph W. Howard ©Spring 2008

Let’s start off by observing some various situations Dr. Joseph W. Howard ©Spring 2008

Let’s start off by observing some various situations Dr. Joseph W. Howard ©Spring 2008

What can we say? • Net Force to START motion • Net Force to

What can we say? • Net Force to START motion • Net Force to STOP motion • Net Force to CHANGE motion, not to continue the motion Dr. Joseph W. Howard ©Spring 2008

Forces and Newton’s Laws of Motion But what ARE FORCES? Dr. Joseph W. Howard

Forces and Newton’s Laws of Motion But what ARE FORCES? Dr. Joseph W. Howard ©Spring 2008

Newton’s First Law • Objects at rest stay at rest unless a “net force”

Newton’s First Law • Objects at rest stay at rest unless a “net force” is applied. • Objects in uniform straight line motion stay in straight line motion unless a “net force” is applied. • Note: Newton’s First Law Does NOT say… • This law does not say that every moving object has a “force” acting on it! • This law does not say an object at rest has “no force(s)” acting on it! Dr. Joseph W. Howard ©Spring 2008

What does a “net Force” cause? What happens when you “force” a change on

What does a “net Force” cause? What happens when you “force” a change on an object? “change in velocity!” Acceleration!!! ? Dr. Joseph W. Howard ©Spring 2008 But what is it proportional too?

Forces cause Acceleration Is it always the same? Same force? Same Acceleration? Objects “resist”

Forces cause Acceleration Is it always the same? Same force? Same Acceleration? Objects “resist” a change……. why? Inertia How do we measure interia? Mass Dr. Joseph W. Howard ©Spring 2008

Mass – The quantity of e matter ( oscal stuff!) in an object is

Mass – The quantity of e matter ( oscal stuff!) in an object is a measure of an object’s inertia. nan Dr. Joseph W. Howard ©Spring 2008

Putting it all together Net FORCE to cause a “change” in motion. (stop, start,

Putting it all together Net FORCE to cause a “change” in motion. (stop, start, change direction, etc…. Any change!) Net Force causes an ACCELERATION How much acceleration depends on the object’s MASS Dr. Joseph W. Howard ©Spring 2008

Newton’s Second Law The acceleration of an object is directly proportional to the net

Newton’s Second Law The acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object. a = Fnet/m OR Fnet = ma Dr. Joseph W. Howard ©Spring 2008 Units of Force? Newtons

The More Mass Something Has, the Harder it is to Get A Significant Change

The More Mass Something Has, the Harder it is to Get A Significant Change in Motion. Resulting Velocity Applied Force Resulting Velocity Dr. Joseph W. Howard ©Spring 2008

More on “net Forces” 2 kg 6 N 7 N 2 kg 6 N

More on “net Forces” 2 kg 6 N 7 N 2 kg 6 N a = F/m = (6 N)/(2 kg) = 3 m/s 2 to the right 6 N a = F/m = (6 N – 6 N)/(2 kg) = 0 m/s 2 15 N a = F/m = (15 N – 7 N)/(2 kg) = 4 m/s 2 to the right Dr. Joseph W. Howard ©Spring 2008

If There are More Than Two Forces, They are Added Together as Vectors Force

If There are More Than Two Forces, They are Added Together as Vectors Force 1 Net Force of Force 1 and Force 2 Mass Force 2 The resultant force is the net force acting on the object. Dr. Joseph W. Howard ©Spring 2008

Friction is a force! It “compels” objects to “change” their motion. In fact, FRICTION

Friction is a force! It “compels” objects to “change” their motion. In fact, FRICTION always opposes motion. Dr. Joseph W. Howard ©Spring 2008

Conceptual Pitfall A 10 kg box is being pushed across the floor at a

Conceptual Pitfall A 10 kg box is being pushed across the floor at a constant velocity of 1 m/s. What is the net force acting on the box? 10 kg 1 m/s Net Force = ZERO Dr. Joseph W. Howard ©Spring 2008

Conceptual Pitfall A bus accelerates by the engine applying a force of 2000 N

Conceptual Pitfall A bus accelerates by the engine applying a force of 2000 N East to the tires for 1 minute. Suddenly the bus encounters a strong wind with a frictional air resistance force of 2000 N West. Which of the following happens? The bus will continue to gain speed The bus has no net force, therefore it stops because of the wind The bus will continue to move with a constant speed The bus will slow down because there is no acceleration Dr. Joseph W. Howard ©Spring 2008

Newton’s First Law • Objects at rest stay at rest unless a “net force”

Newton’s First Law • Objects at rest stay at rest unless a “net force” is applied. • Objects in uniform straight line motion stay in straight line motion unless a “net force” is applied. Dr. Joseph W. Howard ©Spring 2008

Newton’s Second Law The acceleration of an object is directly proportional to the net

Newton’s Second Law The acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object. a = Fnet / m OR Fnet = ma Dr. Joseph W. Howard ©Spring 2008

Newton’s Third Law Whenever one object exerts a force on a second object, the

Newton’s Third Law Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. “To every action there is an equal and opposite re-action. ” Dr. Joseph W. Howard ©Spring 2008

Newton’s 3 rd in Action The force the person exerts on the heavier boulder

Newton’s 3 rd in Action The force the person exerts on the heavier boulder is equal in magnitude but opposite in direction to the force the boulder exerts on the person. EVEN IF THE BOULDER IS BEING PUSHED UPHILL!!! Dr. Joseph W. Howard ©Spring 2008

Wait just a moment. . . I said Weight! What is weight? A measure

Wait just a moment. . . I said Weight! What is weight? A measure of the Force of gravity acting on an object. Weight = (mass) (acceleration of gravity) Weight = (m) (9. 8 m/s 2) Weight = (m) (g) Dr. Joseph W. Howard ©Spring 2008

Wait just a moment. . . Weight = (mass) (acceleration of gravity) Weight =

Wait just a moment. . . Weight = (mass) (acceleration of gravity) Weight = (m) (g) Heavy Object? More force of gravity Lite Object? less force of gravity BUT!!! Each has same acceleration of gravity (9. 8 m/s 2 down) Dr. Joseph W. Howard ©Spring 2008

Distance and Displacement Distance and Displacement Distance andDistance and Displacement Distance and Displacement Distance and
Describing motion Distance and Displacement Distance vs DisplacementDescribing motion Distance and Displacement Distance vs Displacement
Distance Displacement Speed and Velocity Distance l DistanceDistance Displacement Speed and Velocity Distance l Distance
Speed Measuring motion Calculating Speed Speed S distanceSpeed Measuring motion Calculating Speed Speed S distance
Motion Speed What is Speed Speed distance timeMotion Speed What is Speed Speed distance time
Vocabulary Distance Velocity Speed Average Speed Displacement AccelerationVocabulary Distance Velocity Speed Average Speed Displacement Acceleration
CHAPTER 2 Distance vs Displacement Distance How farCHAPTER 2 Distance vs Displacement Distance How far
Displacement vs distance a Distance how far somethingDisplacement vs distance a Distance how far something
DISTANCE VS DISPLACEMENT SPEED VS VELOCITY DISTANCE scalarDISTANCE VS DISPLACEMENT SPEED VS VELOCITY DISTANCE scalar
Displacement vs Distance Distance l Distance d howDisplacement vs Distance Distance l Distance d how
Displacement vs Distance Distance l Distance d howDisplacement vs Distance Distance l Distance d how
Accelerated Displacement and Free Fall Displacement Displacement isAccelerated Displacement and Free Fall Displacement Displacement is
Displacement Reactions Single Displacement Reactions Single Displacement reactionDisplacement Reactions Single Displacement Reactions Single Displacement reaction
MEASURING MOTION DISPLACEMENT SPEED AVERAGE SPEED VELOCITY RESULTANTMEASURING MOTION DISPLACEMENT SPEED AVERAGE SPEED VELOCITY RESULTANT
One Dimensional Motion Distance and Displacement Speed andOne Dimensional Motion Distance and Displacement Speed and
Motion Review Distance Displacement Scalar vs Vector SpeedMotion Review Distance Displacement Scalar vs Vector Speed
Motion Distance and Displacement Speed and Velocity AccelerationMotion Distance and Displacement Speed and Velocity Acceleration
Motion Distance Displacement Speed average and instantaneous VelocityMotion Distance Displacement Speed average and instantaneous Velocity
MOTION IN ONE DIMENSION Distance Displacement Speed andMOTION IN ONE DIMENSION Distance Displacement Speed and
SPEED VELOCITY AND ACCELERATION Motion Distance Displacement FrameSPEED VELOCITY AND ACCELERATION Motion Distance Displacement Frame
Distance displacement speed acceleration State the obvious motionDistance displacement speed acceleration State the obvious motion
Introduction to Motion Distance vs Displacement Speed vsIntroduction to Motion Distance vs Displacement Speed vs