forces. 9/7/2006isp 209 - 2b2 which vehicle exerts a greater force ― the tow truck or the car?
TRANSCRIPT
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FORCES
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ISP 209 - 2B 29/7/2006
Which vehicle exerts a greater force ― the tow truck or the car?
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What is a force?
• A push or a pull
• When one object pushes or pulls another object, you say that the first object exerts a force on the second object.
• Let’s practice. What forces are at play around you?
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What forces are exerted?
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What forces are exerted?Playing catch with a medicine ball
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ISP 209 - 2B 69/7/2006
Playing catch with a medicine ball
A throws the ball and B catches it. four forces
When A throws the ball he exerts a force on the ball (toward the right) and the ball exerts a force on him so he recoils (toward the left).
A B
When B catches the ball he exerts a force on the ball (toward the left to stop it) and the ball exerts a force on him so he is knocked back (toward the right).
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Scalars and Vectors
• Are both quantities
• BUT…..• Scalars are fully described by
magnitude (magnitude= number)
• Vectors are fully described by both magnitude(number) and direction
Let’s take a minute to discuss….
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QUANTITY SCALAR or VECTOR?
5 m
30 m/sec, East
5 mi., North
20 Degrees Celsius
256 bytes
4000 calories
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QUANTITY SCALAR or VECTOR?
5 m Scalar
30 m/sec, East Vector
5 mi., North Vector
20 Degrees Celsius Scalar
256 bytes Scalar
4000 calories Scalar
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What is force categorized as?
• Force is described by the strength and direction in which it acts.
• Therefore,• Force is a VECTOR
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The strength of force is measured in…
• The SI unit called the Newton (N)• One Newton is the amount of force required
to give a 1-kg mass an acceleration of 1 m/s/s. • Thus, the following unit equivalency can be
stated:
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Combining Forces
• Often, more than one force acts on an object at a time.
• Net force is the combination of all forces acting on the object
• What does the net force determine?– Motion– direction
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Net force Practice
• For each diagram, write the net force and direction.
HINT: The net forcealways acts in the directionof the greater force.
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Balanced forces
• Equal forces acting on one object in opposite directions.
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Balanced Forces
• Balanced forces result in equilibrium• How can I make this box in equilibrium?
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Unbalanced Forces
• Unbalanced forces result when the forces exerted on an object are not equal.
• Unbalanced forces acting on an object result in a net force and cause a change in the object’s motion.
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Free-Body Diagrams
• Free-body diagrams are diagrams used to show the relative magnitude and direction of all forces acting upon an object in a given situation.
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Draw a free body diagram
• A physics book is sitting on a table and is pushed 10 N to the right. The opposing frictional force is 7 N.
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ISP 209 - 2B 199/7/2006
Resolution: Consider each part separately, and don’t forget that there are other forces acting.
So how can they start moving, or accelerate?
A puzzleHorse and Cart
The horse pulls the cart with a force A (to the right).
According to Newton, the cart pulls the horse with a force –A (to the left).
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Homework
• Read Introduction of Forces notes• Give 3 examples of force for each of the
following: (YOUR OWN EXAMPLES!)– Gravity– Tension– Friction– Drag/Air resistance