* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Physics 1710 Chapter 5: Laws of Motion—I
Survey
Document related concepts
Jerk (physics) wikipedia , lookup
Modified Newtonian dynamics wikipedia , lookup
Fictitious force wikipedia , lookup
Brownian motion wikipedia , lookup
Inertial frame of reference wikipedia , lookup
Classical mechanics wikipedia , lookup
Newton's theorem of revolving orbits wikipedia , lookup
Hunting oscillation wikipedia , lookup
Centrifugal force wikipedia , lookup
Rigid body dynamics wikipedia , lookup
Work (physics) wikipedia , lookup
Seismometer wikipedia , lookup
Classical central-force problem wikipedia , lookup
Centripetal force wikipedia , lookup
Transcript
Physics 1710 Chapter 5: Laws of Motion—I Quiz: What lateral acceleration does a pilot experience who is flying a jet at 350 m/s in a 1.00 km banked turn? v a = v 2/R a = (350. m/s) 2 /1000. m = 122. m/s/s = 12 g. Wow! R Physics 1710 Chapter 5: Laws of Motion—I Isaac Newton (1642 –1727) • Published Principia • 1687 • At age 45 Physics 1710 Chapter 5: Laws of Motion—I 1′ Lecture • Newton’s Laws of Motion are: Acceleration (or deceleration) occurs if and only if there is a net external force. a = F/m [Note this is a vector eqn.] The force exerted by a first object on a second is always equal and opposite the the force exerted by the second on the first. F12 = - F21 Physics 1710 Chapter 5: Laws of Motion—I 1′ Lecture –continued (30″ more) • Weight is the force of gravity equal to the mass of the object. g times • g =9.80 N/kg • The force of friction is opposed to the motion of a body and proportional to the normal force. • Free body diagrams are sketches of all the forces acting on a body. Physics 1710 Chapter 5: Laws of Motion—I Aristotle (384-322 BC) • Wrote Physica • Thought that force causes motion. • i.e. F → v • Error: v ≠ 0, but F =0 Physics 1710 Chapter 5: Laws of Motion—I Laws of Motion 1st Law: An acceleration is caused by a net external force. Subtleties: No net force ⇆ no acceleration. Acceleration is the secret to understanding motion. Cf. Aristotle. Physics 1710 Chapter 5: Laws of Motion—I First Law of Motion (implications) • Equilibrium suggests ∑ F = 0. • Force is a vector: [ F, not F] • “Nature is conservative;” inertia is the tendency to resist a change in the status quo. [ Φ \ Ω \ Δ] • An inertial frame of reference is one that is not accelerating. [ a1 = a2 ] Physics 1710 Chapter 5: Laws of Motion—I Balloon Drop Physics 1710 Chapter 5 The Laws of Motion Terminal Velocity Weight is the force due to gravity • Fg = g‧m; g =9.80 N/kg Air resistance depends on the wind velocity • Fv ≈ - γA v 2 •Total ∑ F = Fg+ Fv = 0 • ∑ F = gm – γAvT2 = 0 • vT = √[g‧m/ γA] Implications? Physics 1710 Chapter 5: Laws of Motion—I 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 -0.5 Velocity (m/s) -1 Terminal Velocity -1.5 -2 -2.5 -3 -3.5 -4 Time (sec) 0.45 Physics 1710 Chapter 5: Laws of Motion—I 1.05 Position (m) 1 0.95 0.9 At Terminal Velocity Free Fall 0.85 0.8 0 0.05 0.1 0.15 0.2 0.25 Time (sec) 0.3 0.35 0.4 0.45 Physics 1710 Chapter 5: Laws of Motion—I Balloon Drop vT = √[g‧m/γA] vT ∝ √m Physics 1710 Chapter 5: Laws of Motion—I Terminal Velocity Weight is the force due to gravity •vT = √[g‧m/kA] • Heavy (i.e. massive) objects fall faster than lighter ones. For example g‧m > 100 kA →vT > 10 m/s, a hard fall. • A parachute slows you down. kA > g‧m/100 →vT < 10 m/s, not too bad Physics 1710 Chapter 5: Laws of Motion—I Why does a projectile follow a parabolic trajectory? There is only a Force acting in the vertical (downward) direction. Therefore, the is only a downward acceleration. Physics 1710 Chapter 5: Laws of Motion—I Concept Test: A spaceship in deep space is moving sidewise initially when it fires it’s impulse engine, producing a constant thrust. Sketch the trajectory of the spacecraft. Physics 1710 Chapter 5: Laws of Motion—I Concept Test: A spaceship in deep space is moving sidewise initially when it fires it’s impulse engine, producing a constant thrust. Sketch the trajectory of the spacecraft. It then turns off its engine; what happens then? Physics 1710 Chapter 5 The Laws of Motion There are two kinds of mass ( assumed to be equivalent): gravitational mass: Fg = g m inertial mass: a ∝ 1/m a1 /a2 = m2 /m1 Mass is an inherent property of matter, independent of the surroundings and the method used to measure it. Physics 1710 Chapter 5 The Laws of Motion Summary • Newton’s 1st Law of Motion is: A body at rest will remain at rest and a body in motion will remain in the same state of motion unless acted upon by an external unbalanced force. That is: force causes acceleration.