Contact Force
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Gravity, Normal Force, and Mechanical Advantage: An Introduction to Forces and Equilibrium, Slides of Physics
An introduction to various forces at play, including gravity, normal force, and tension, as well as the concept of mechanical advantage. It covers the basics of forces acting on objects at rest, the role of normal force, and the use of inclined planes and pulleys to reduce the force required for lifting. Students will also learn how to calculate net forces and find components of gravity.
Typology: Slides
2012/2013
1 / 12
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Contact Force
Gravity at Rest
The force of gravity acts onall objects all the time.
If an object is at rest, the lawof inertia says that the netforce is zero.
There must be a forceopposite to gravity thatcancels it out.
Fgrav
mg
F^
=^
F
grav
mg
Normal Force and Weight
The normal force pushing upagainst gravity can be measured.
We measure weight with a scalethat measures normal force.
Weight is a force, not a mass.
Pounds measure weight, soforce (not mass) can bemeasured in pounds.
Forces on a Slope
F^ N
Draw the forces acting onthe block.•
The force of gravity pointsdown with magnitude Fg
= mg
•^
The normal force
F
N^
points
away from the surface of theinclined plane.
-^
An applied force
F
app
holds
the block in place.
^ mg
Fg
F^ app
Mechanical Advantage
The inclined plane has beenused as a machine forcenturies.
Pushing a block up anincline is easier than lifting.
The ratio of the force to liftdirectly compared to theforce using the incline is the mechanical advantage
mg
^
sin
sin
mg
mg
sin
mg
Tension Force
A taut rope has a forceexerted on it.
If the rope is lightweight andflexible the force is uniformover the entire length.
This force is called
tension
and points along the rope.
Tension acts on both ends.
Fg
mg
FT
Fg
mg
FT -F
T
forces onthe rope
forces onthe ball
Equilibrium in One Dimension
Two weights are hungsupported by strings.•
On the lower block the twoforces balance:
F
T^2
m
g 2
•^
On the upper block thereare three:
F
T^1
m
g + F 1
T^2
•^
FT
1
m
1
+ m
g
The upper string has moretension than the lower string.
m
1
FT
m
g 1
3 forces on the upper block
FT
m
2
m
g 2
FT
2 forces on the lower block
Pulley
A pulley uses tension totransfer a force to anotherdirection.
m
1
m
2
m
1 m
1
m
2 m
2
Frope
Ffr
Frope Fg
FT
FT
forces on block 1
forces on the rope forces on block 2