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Chapter 4 Forces and Newton’s Laws of Motion. Motion and Newton’s first law What is a force? Identifying forces Newton’s second law Free-body diagrams Newton’s third law. Topics:. Sample question:. - PowerPoint PPT Presentation
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Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
• Motion and Newton’s first law
• What is a force?
• Identifying forces
• Newton’s second law
• Free-body diagrams
• Newton’s third law
Chapter 4Forces and Newton’s Laws of Motion
Topics:
Sample question:These ice boats sail across the ice at great speeds. What gets the boats moving in the first place? What keeps them from going even faster?
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Example
An elevator, lifted by a cable, is going up at a steady speed. • Identify the forces acting on the elevator.
• Is FT,cable => elevator greater than (A), equal to (B), or less than
Fg,Earth => elevator (C)? Or is there not enough information to tell
(D)?
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Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Checking Understanding
10-year-old Sarah stands on a skateboard. Her older brother Jack starts pushing her backward and she starts speeding up. The force of Jack on Sarah is
A. greater than the force of Sarah on Jack.B. equal to than the force of Sarah on Jack.C. less than the force of Sarah on Jack.
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Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
10-year-old Sarah stands on a skateboard. Her older brother Jack starts pushing her backward and she starts speeding up. The force of Jack on Sarah is
B. equal to than the force of Sarah on Jack.
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Answer
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
A Short Catalog of Forces: Weight w
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Spring Force Fsp
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Tension Force rT
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Normal Force rn
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Friction fk and rfs
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Drag and Thrust rD
rFthrust
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Example 1
A block is dragged uphill by a rope. Identify all forces acting on the block.
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Example 2
The cable at left exerts a -30 N force. • Write the equation for the sum of the forces in the x-direction.
What is the value of FT2? • Write the equation for the sum of the forces in the y-direction.
What is the force of gravity acting on the ball?
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30
T2
T1
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Exercise
A ball, hanging from the ceiling by a string, is pulled back and released. Identify the forces acting on it just after its release.
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Newton’s Second Law
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Newton 2 Demonstrations
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Newton’s Third Law
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Newton’s 3rd Law Demonstrations
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Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Newton’s Laws of Motion
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Newton 0th LawObjects are dumb - They have no memory of the past and cannot predict the future. Objects only know what is acting directly on them right now
Newton's 1st LawAn object that is at rest will remain at rest and an object that is moving will continue to move in a straight line with constant speed, if and only if the sum of the forces acting on that object is zero.
Newton's 2nd Lawacceleration of an object = sum of forces acting on that object / the mass of the object
Newton's 3rd LawRecall that a force is an interaction between two objects. If object A exerts a force on object B then object B exerts a force on object that is in the opposite direction, equal in magnitude, and of the same type.
