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.
Slide 4-19
Forces and Two Books
upper book
low er book
A. Draw a Force Diagram for each book
B. What type of force does the upper book exert on the lower
book? (e.g., frictional, gravitational, etc.)
C. Rank the forces in the two force diagrams from largest to
smallest
Slide 4-19
Scales and Elevators (Apparent Weight)
Suppose a person with a mass of 60 kg is in an elevator
standing on a scale.
Use a system schema and free body diagrams of the scale
and the person to determine what the scale would read for
the following situations:
A. If the elevator is descending at 4.9 m/s.
B. If the elevator has a downward acceleration of
4.9 m/s/s.
C. If the elevator has an upward acceleration of
4.9 m/s/s.
Slide 4-19
Half Atwood-Machine (Working with Systems)
A block of mass M1 is sitting on a frictionless table. It is
connected by a massless string over a massless and
frictionless pulley to another block of mass M2.
(a) Build free-body diagrams for each of the masses and write
equations of motion for each object. Use the coordinate x1 shown
in the figure for the position of mass M1 and coordinate y2 shown
in the figure for the position of mass M2.
(b) Use these equations of motion to obtain the acceleration of the two
objects. Explicitly state any conditions that you are applying to
solve the equations.
Slide 4-19
Parking on a Hill
A. If you park on a hill with a 10 degree slope with the car
held by the parking brake, what is the magnitude of the
frictional force that holds your car in place?
(Work in symbols)
B. The coefficient of static friction between your car's
wheels and the road when wet is 0.30. What is the
largest angle slope on which you can park your car in the
rain so that it will not slide down the hill?
C. The coefficient of kinetic friction between your wheels
and the wet road surface is 0.25. If someone gave your
your car a push on the wet hill and it started sliding
down, what would its acceleration be?
Slide 4-19