Transcript Equilibrium
Equilibrium Force Force is Force is not A push or pull on an object. Energy. A vector with magnitude and direction. Power. Momentum. Velocity. Fundamental Forces Gravity is a fundamental force. It acts upon objects from a distance away from the source (such as the Earth). There are two other fundamental forces. Electroweak force is common in everyday life. • • • • Electricity Magnetism Light Radioactive decay Nuclear force is uncommon in everyday life. • Nuclear fission (nuclear power plants) • Nuclear fusion (stars) Contact Forces Many forces are due to contact between objects. • • • • Kick a ball Push with a bulldozer Tug from a rope Friction due to the ground The actual force is electricity, but the atoms are so small we can treat the forces as coming from contact by larger objects. Newton’s Laws Ancient scientists looked to the natural properties of objects. • Motion was a result of the object’s properties. Newton defined motion based on forces acting from outside an object. • Motion was the result of external forces. Three laws were used to define the behavior of forces on objects. First Law: Law of Inertia 1 An object continues at rest, or in uniform motion in a straight line, unless a force is imposed on it. This describes constant velocity, including zero. No change means no force, and vice versa. no force rocket constant velocity Zero Net Force An object at rest with no net force is in static equilibrium. The net force is due to the sum of forces acting on the object. • The forces are vectors Fnet F 0 Static Forces An advertising sign weighs 210 N. It is supported from a post with a horizontal beam, and by a chain making an angle of 35 from the horizontal. What is the force in the chain? q = 35º Newton Legal W = 210 N Vector Forces With no motion, forces must sum to zero. Identify forces on the sign. • C is the force on the chain • B is the force on the beam • W is the weight Vector sum is zero. B C W W C B Force Components To find the values, use components Find the vertical components for the force on the chain. • • • • q = 35º Cx Cy Bx Wy = -210 N Cy = C sinq Wy = -210 N 0 = Cy + Wy = C sinq + Wy C = -Wy / sinq = 370 N Use horizontal components for the force on the beam. • 0 = Bx + Cx = Bx + (-C cosq) • Bx = C cosq = 300 N Constant Velocity Constant velocity means no change in motion. v0 Dynamic equilibrium applies in states of constant, nonzero velocity. Zero net force used here: • FN + Fg + Fy = 0 • Fx + Ffr = 0 FN Ffr Fx Fg Fy next