Last Lecture: Projectile Motion
Lecture 5
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¾
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Horizontal motion
Vertical motion
Force and Motion.
Mass and Weight,
Free Body Diagrams
(HR&W, Chapter 5)
http://web.njit.edu/~sirenko/
Physics 105; Summer 2006
Lecture 5
Andrei Sirenko, NJIT
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Lecture 5
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Projectile Motion; General Case
Trajectory and horizontal range
Newton’s
Laws
I.
If no net force acts on a body, then the body’s velocity cannot
II.
III.
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change.
The net force on a body is equal to the product of the body’s mass
and acceleration.
When two bodies interact, the force on the bodies from each
other are always equal in magnitude and opposite in direction.
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Objectives
Forces:
Gravitational Force:
¾
• By the end of Week we should be able to
– Formulate Newton’s laws in our own words
– Draw free-body-diagrams (FBDs) for a given
problem
– Explain the difference between static and
kinetic frictional force
– List a few reference frames where Newton’s
laws do not apply
Archimedes Force
¾
Friction Force:
¾
Tension Force
¾
Spring Force
¾
¾
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F = mg
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Normal Force
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Force is a vector. Units: [Newton]
Forces:
1 N = 1 kg • 1 m/s2
Force has direction and magnitude
Mass connects Force and Acceleration
Mass is a measure of inertia.
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Forces:
Gravitational Force:
F = mg
¾
Archimedes Force
¾
Friction Force:
¾
Tension Force
¾
Spring Force
¾
¾
Normal Force
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Gravitational Force:
F = mg;
g = 9.8 m/s2
R = 6,400 km
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EXAMPLES of Free Body Diagrams
Picture of Situation
FBD
mg
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mg
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EXAMPLE
5N
θ
θ = 30º
Find F3 so that a = 0
F net = F1 + F2
F net = ma
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10N
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EXAMPLE
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FBD
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How do we jump ?
Static and Kinetic Friction
Static frictional force
Kinetic frictional force
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Uniform Circular Motion
Kinetic Friction
Centripetal acceleration
Top view:
Kinetic frictional force:
Skid marks are 290 m long!
µk = 0.6 and a = const. How
fast was the car going when
the wheels became locked?
Period
Centripetal force : F = ma
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QZ #5
Name, ID #, Section #
Problem 1:
What is the acceleration (in unit vectors notation) of a
particle with m =2 kg due to a combination of two
forces:
F1= (2N)i+(2N)j-(3N)k and F2= (-2N)i+(2N)j+(6N)k.
Problem 2:
What is the magnitude of the acceleration vector?
Problem 3:
What is the magnitude of the Net Force ?
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