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The concepts of various forces, including field forces (gravity, electrical, magnetic) and contact forces (normal force, friction). It also covers the concepts of static and kinetic friction, and their relationship to the forces of friction. Examples and formulas for calculating the magnitudes of these forces, as well as the effect of strings on force direction. It also discusses newton's second law and the concept of inertia.
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Field forces – forces due to interaction FIELD with can act through empty space over long distance
Forces due to physical contact with other object
Gravity
Electrical
Magnetic
Two objects attract due to gravitational force.
For example, the earth attracts other objects
g is the gravitational constant 9.8 m/s 2
Magnitude of gravitational force is called the weight of the object
Weight = | F g |= mg
Strings allow us to change the direction in which the force is applied. The force applied on both ends of a string should be equal, otherwise the string accelerates
In the figures shown, all the green boxes have the same mass and all the pulleys are identical. In which case is the tension in the string greater?
Need force to accelerate Law applies to forces exerted ON individual object
Larger Mass, less acceleration for same force
More than one force can be applied to one object: vector sum of all forces yields net force on object!
Σ F = ma
Units of Force? (^) 2 Derived units: Newton (N) 1N =
m kg s
F = ma
An object is held in place by static friction on an inclined surface. The angle of inclination is increased until the object starts moving and now experiences dynamic friction. If the surface is no longer increased once the object starts moving, then the object
A constant force is exerted on a cart that is initially at rest on an air track. Friction between the cart and the track is negligible. The force acts for a short time interval and gives the cart a certain final speed. To reach the same final speed with a force that is only half as big, the force must be exerted on the cart for a time interval (from E. Mazur, “Peer Instruction: A users manual”, Prentice Hall 1997)
The stronger force
