dynamics zwhy things move yaccelerations caused by forces
TRANSCRIPT
Forces
Non Contact Contact
Pushes PullsGravitational Electromagnetic Nuclear
Normal Friction Tension
M T f N
WElectric Magnetic
perpendicular to surface
Newton’s Laws of Motion
1st Law:•no net force no acceleration•no acceleration no change in
motion•Objects at rest will remain at rest
and objects in motion will remain in motion at constant speed, in a straight line, unless acted on by a net force
Newton’s Laws of Motion
1st Law:•no net force no acceleration•no acceleration no change in
motion•Objects at rest will remain at rest
and objects in motion will remain in motion at constant speed, in a straight line, unless acted on by a net force
Mass
Measure of how much ‘stuff’
Measure of how hard it is to speed up or slow down the object
Mass and weight are very different
Putting it all together
a MFnet
Constant *
Newton is defined such that constant = 1.
a MFnet
aMFnet
Newton’s 2nd Law
Newton’s Laws
1st
Objects at rest will stay at rest and objects in motion will stay in motion, at a constant speed, in a straight line, unless acted on by a net force.
2nd
Objects with a non-zero net force accelerate in the direction of the net force via Fnet = ma
Poor Gary:
Gary has a major problem. After studying Newton’s Third Law in his physics class, he has convinced himself of its validity. Unfortunately, he has convinced himself while sitting in a closed room with a single door. He reasons to himself: “If I push on the door to go out, Newton’s 3rd Law tells me that the door is going to push back with an equal force. That force is going to cancel the force that I push with. Even if I push as hard as I can, that door is going to push back just as hard! Oh no! I’m stuck in this room! Why did I ever take physics!”
The famous bug problem:
• A bug splats on the windshield of a car moving at 100 mph. Which feels the greater force, the car or the bug?
• Which has the worst day?
Apparent weight
• measured as the reading of the scale
• equal to the normal force of the scale on your feet
• equal to weight for a=0
Orbit
“…there is an art to flying, or rather a knack. The knack lies in learning how to throw yourself at the ground and miss.”
– Douglas AdamsLife, The Universe, and Everything
Uniform Circular motion
Which direction is the instantaneous velocity?
Which direction is the acceleration?
Uniform Circular motion
WE,B
TS,B
Freebody
Which direction is the instantaneous velocity?
Which direction is the acceleration?
Uniform Circular motion
Which direction is the instantaneous velocity?
Which direction is the acceleration?
WE,B
TS,B
Freebody
Uniform Circular motion
Which direction is the instantaneous velocity?
Which direction is the acceleration?
Freebody
Aren’t we missing something?
Ty
WE,BTx
THE CENTRIFUGAL FORCE!CENSORED
Centrifugal. adj. Moving or directed away from the center.
Ty
WE,BTx
CENSORED
Forces
Non Contact Contact
Pushes PullsGravitational Electromagnetic Nuclear
Normal Friction Tension
M T f N
WElectric Magnetic
perpendicular to surface
Ty
WE,BTx
THE CENTRIFUGAL FORCE!CENSORED
Centrifugal. adj. Moving or directed away from the center.
The centri*&%#l force DOES NOT EXIST!For uniform circular motion the net force
must be towards the center of the circle.Therefore: The acceleration is ‘center
seeking’
CENSORED
CENSORED
Ty
WE,BTx
THE CENTRIFUGAL FORCE!CENSORED
Centrifugal. adj. Moving or directed away from the center.
The centri*&%#l force DOES NOT EXIST!For uniform circular motion the net force
must be towards the center of the circle.Therefore: The acceleration is
centripetal
CENSORED
CENSORED
The swinging bucket of death
A
B
CI
Physics
Draw freebody diagrams for the water at points A, B, and C.