Transcript Powerpoint for today

Newton's Laws of Motion
Newton 0th Law
Objects 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 Law
An 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 Law
acceleration of an object = sum of forces acting on that object / the mass of the
object
Newton's 3rd Law
Recall 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.
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Slide 4-19
Newton’s 3rd Law Demonstrations
A.
FA=>B > FB=>A
B.
FA=>B < FB=>A
C.
FA=>B = FB=>A
D.
Not enough information given to tell
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Slide 4-19
Impulse
The force of the foot
on the ball is an
impulsive force.
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Slide 9-8
Graphical Interpretation of Impulse
J = Impulse = area under
the force curve  Favg t
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Slide 9-9
Momentum
Momentum is the product of an object’s mass and its velocity:


p = mv
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Slide 9-10
The Impulse-Momentum Theorem
Impulse causes a change in momentum:




J =pf - pi = ∆p
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Slide 9-11
Clicker Question
1. Impulse is
A. a force that is applied at a random time.
B. a force that is applied very suddenly.
C. the area under the force curve in a
force-versus-time graph.
D. the interval of time that a force lasts.
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Slide 9-2
Answer
1. Impulse is
C. the area under the force curve in a
force-versus-time graph.
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Slide 9-3
Gravitational Force & Coordinate Systems
A. Fg,y = -- mg
B. Fg,y = -- mg sin(theta)
C. Fg,y = mg cos(theta)
D. Fg,y = -- mg cos(theta)
E.Can’t tell what Fg,y is
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Slide 4-19
Samantha the Skier
Samantha is skiing at Taos on an intermediate slope that
makes a
25 degree angle with the horizontal.
A. Assuming Friction is too small to be accounted for, what
is Samantha’s acceleration?
B. After Samantha has gone 100 m, what is her velocity?
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Slide 4-19