PHYS 1051 Lecture Notes - Lecture 6: Friction, Acceleration, Apparent Weight
Ch. 6 Application of Newton’s Laws
Notes
General Notes
1st Law
oSummation of forces=0
Rest
Constant velocity
2nd Law
oSummation of forces=Ma
oUnbalanced forces cause accelerations
oAcceleration is directly proportional to summation of forces
oAcceleration is inversely proportional to mass
Inclines
Rotate the axis of the box on the incline
Form rectangles of the Fx and Fy components
F(perpendicular), F(parallel), and Fw(gravity)=mg
oIf acceleration is bigger, the force is going down
Problem types:
oContact forces
oObjects connected by strings
Friction- a force that opposes the relative motion of surfaces which are in contact
Static friction- when things are at rest but still have friction
Equation of a straight line: y=mx
Objects have static and kinetic friction
μs and μk are NOT forces, but they are ratios of frictional forces to normal forces
μ is dimensionless so it has no units
Circular Motion
Assume constant speed
Constant speed and acceleration but not constant velocity
Equations:
oSummation of forces=mac
oSummation of forces=(mv^2/r)
oAc=(v^2/r)
Centripetal acceleration
Centripetal force-unbalanced force directed toward the center of a circular path
Velocity is always tangent to the curve of a circle and perpendicular to the radius
IF velocity and acceleration are perpendicular, velocity is changing direction
Apparent weight is simply normal force
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Document Summary
2nd law: summation of forces=ma, unbalanced forces cause accelerations, acceleration is directly proportional to summation of forces, acceleration is inversely proportional to mass. Rotate the axis of the box on the incline. Form rectangles of the fx and fy components. F(perpendicular), f(parallel), and fw(gravity)=mg: if acceleration is bigger, the force is going down. Problem types: contact forces, objects connected by strings. Friction- a force that opposes the relative motion of surfaces which are in contact. Static friction- when things are at rest but still have friction. S and k are not forces, but they are ratios of frictional forces to normal forces. Is dimensionless so it has no units. Constant speed and acceleration but not constant velocity. Equations: summation of forces=mac, summation of forces=(mv^2/r, ac=(v^2/r) Centripetal force-unbalanced force directed toward the center of a circular path. Velocity is always tangent to the curve of a circle and perpendicular to the radius.
