2 ForcePush or pullThe cause of an acceleration or the change in an object’s velocity (pg. 124)
3 Force can act through contact or distance (pg. 125) Contact force- force that arises from the physical contact of two objectsEx: pulling a spring, pull a wagon, pushing carField force- force that can exist between objects, even in the absence of physical contact between the objectsEx: gravity, electrical charges
4 Applied ForceForce which is applied to an object by a person or another objectFapp: student pushing or pulling a desk across the room
5 Gravity ForceForce 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 gravityWhere acceleration due to gravity is 9.8 m/s2
6 Normal ForceThe 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 bookFnorm
7 Friction ForceThe 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
8 Air Resistance ForceForce which acts upon objects as they travel through air (often observed to oppose the motion of an object)Fair : skydiver, or downhill skier
9 Tension ForceForce which is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends.Ftens:
10 Spring ForceForce exerted by a compressed or stretched spring upon any object which is attached to it.Fspring:
11 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
12 Problem 1A book is at rest on a table top. Draw the free body diagram that depicts this action.
13 Problem 2An egg is free-falling from a nest in a tree. Neglect air resistance. Draw a free-body diagram showing the forces involved
14 Problem 3A 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…
15 Problem 4A 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.