* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download document 8128429
Survey
Document related concepts
Center of mass wikipedia , lookup
Hooke's law wikipedia , lookup
Relativistic mechanics wikipedia , lookup
Coriolis force wikipedia , lookup
Modified Newtonian dynamics wikipedia , lookup
Classical mechanics wikipedia , lookup
Fictitious force wikipedia , lookup
Equations of motion wikipedia , lookup
Seismometer wikipedia , lookup
Newton's theorem of revolving orbits wikipedia , lookup
Rigid body dynamics wikipedia , lookup
Centrifugal force wikipedia , lookup
Classical central-force problem wikipedia , lookup
Transcript
Ch4 Laws of Motion 4.2,3,4 Newton’s law Isaac Newton(1642-1727) He studied various subject in his life: Calculus law of gravitation, law of motion Optics Alchemy Theology “If object 1 and object 2 interact, the force F12 Example exerted by object 1 on object 2 is equal in magnitude but opposite in direction to the force 2 F21 exerted by object 2 on object1” examples 1.Force: One pushes a chair Reaction force: The chair pushes the person. 2.Force: Earth pulls a person Reaction force: A person pulls Earth. Newton’s First law 3.Normal force is not the reaction force of “An object moves with a velocity that is constant weight of an object. in magnitude and direction unless a non-zero Action and reaction forces acts on different net force acts on it” object. Galileo discovered the first law of motion and Newton restated it in his law of motion. Galileo’s thought experiment SI unit N = kg m/s2 B A 1 n2 n1 F T T w1 w2 m 3.2 free-body diagram. Diagram of forces acting on one object. 3.3 types of forces Newton’s Second law Reaction forces does not appear since it acts on There are four fundamental forces in the “The acceleration a of an object is directly a different object. nature, but we will discuss the fundamental proportional to the net force acting on it and Drawing a free body diagram. forces later time. inversely proportional to its mass” 1. Isolate an object. Some forces have names since they appear so In many problems, objects are connected. You often and we will discuss about these forces. F ma need to draw a separate diagram for each Weight (w) Force and mass are defined by this equation. object. The gravitational force acting on an object. Force is a vector so we can compute x-,y- and z- 2. Find the forces acting on the object. w = mg direction independently. Tension(T) inertia: tendency of an object to continue in its 3. Draw force vectors and label them according Pulling force exerted by each end of string, rope original state of motion. to the step 2. or cable. Mass: measure of inertia. This is one definition Normal force(n) of mass. Force exerted by a surface. Its direction is always perpendicular to the surface and Newton’s Third law opposite to the force acting on the surface. Friction(f) Force resists a motion on a surface or through a viscous medium. The direction of friction is opposite the actual motion or impending motion. When an object is at rest or moving at a constant velocity, f = - F. Thus, friction has the same magnitude as the force exerted and opposite direction in this case. Static friction When an object is stationary, f s n In this case f is equal magnitude and opposite direction of the force exerted. μs is the coefficient of static friction. When an object is in motion. f k n Where μk is the coefficient of kinetic friction. As you can see in the equations, friction is proportional to the normal force exerted by the surface on the object. The coefficient of the friction is nearly independent of the area of contact between the surfaces. A traffic light weight 1.00 x 102 N hangs from a vertical A woman weight a fish with a spring scale attached to cable tied to two other cables that are fastened to the ceiling of an elevator, as shown in figures. While the elevator is at rest, she measured a a support. The upper cables make angles of 37.0° weight of 40.0 N. and 53.0° with the horizontal. Find the tension in each of the three cables. (a) What weight does the scale read if the elevator accelerates upward at 2.00 m/s2? (b) What weight does the scale read if the elevator accelerates downward at 2.00 m/s2? (c) If the elevator cable breaks, what does the scale read? Suppose a block with a mass of 2.50 kg is resting on a The objects of mass m1 and m2, with m2 >m1, are connected by a light, inextensible cord and hung ramp. If the coefficient of static friction between over a frictionless pulley, as in Figure. Both cord the block and ramp is 0.350, what maximum and pulley have negligible mass. Find the angle can the ramp make with the horizontal magnitude of the acceleration of the system and before the block starts to slip down the tension in the cord.