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TYPES OF FORCESFree Body Diagrams
Force
Push or pull The cause of an acceleration or the
change in an object’s velocity (pg. 124)
Force can act through contact or distance (pg. 125)
Contact force- force that arises from the physical contact of two objects Ex: pulling a spring, pull a wagon, pushing car
Field force- force that can exist between objects, even in the absence of physical contact between the objects Ex: gravity, electrical charges
Applied Force
Force which is applied to an object by a person or another object Fapp: student pushing or pulling a desk across
the room
Gravity Force
Force with which the earth, moon, or other massively large object attracts another object towards itself. (By definition, this is the weight of the object) Fgrav: = mass x acceleration due to
gravity Where acceleration due to gravity is 9.8
m/s2
Normal Force
The support force exerted upon an object which is in contact with another stable object. Ex: book resting on a table, the table is
exerting an upward force upon the book in order to support the weight of the book
Fnorm
Friction Force
The force exerted by a surface as an object moves across it or makes an effort to move across it Ffrict = (“mu”) (fnorm) Sliding and static friction
Air Resistance Force
Force which acts upon objects as they travel through air (often observed to oppose the motion of an object)
Fair : skydiver, or downhill skier
Tension Force
Force which is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends. Ftens:
Spring Force
Force exerted by a compressed or stretched spring upon any object which is attached to it. Fspring:
Coefficient of Friction
The 'coefficient of friction' (COF), symbolized by the Greek letter µ “mu”, is a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together. The coefficient of friction depends on the materials used; for example, ice on steel has a low coefficient of friction, while rubber on pavement has a high coefficient of friction. Coefficients of friction range from near zero to greater than one – under good conditions, a tire on concrete may have a coefficient of friction of 1.7
“mu” =coefficient of friction
Problem 1
A book is at rest on a table top. Draw the free body diagram that depicts this action.
An egg is free-falling from a nest in a tree. Neglect air resistance. Draw a free-body diagram showing the forces involved
Problem 2
Problem 3
A flying squirrel is gliding (no wing flaps) from a tree to the ground at constant velocity. Consider air resistance. A free body diagram for this situation looks like…
Problem 4
A rightward force is applied to a book in order to move it across a desk. Consider frictional forces. Neglect air resistance. Construct a free-body diagram. Let’s see what this one looks like.
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