Newton’ s First lay An object subject to no external forces moves with a constant velocity if viewed from an inertial reference frame If no forces act there is no acceleration The above statement can be thought of as the definition of inertial reference frames An IRF is a reference frame that is not accelerating(or rotating) with respect to the fixed stars If one IRF exists, infinitely many exist since they are related by any arbitrary constant velocity vector Physics 121: Lecture 7, Pg 11
Physics 121: Lecture 7, Pg 11 Newton’s First Law An object subject to no external forces moves with a constant velocity if viewed from an inertial reference frame. If no forces act, there is no acceleration. The above statement can be thought of as the definition of inertial reference frames. An IRF is a reference frame that is not accelerating (or rotating) with respect to the “fixed stars”. If one IRF exists, infinitely many exist since they are related by any arbitrary constant velocity vector!
Is Storrs a good IRF? Is Storrs accelerating ? YES! Storrs is on the earth The Earth is rotating What is the centripetal acceleration of storrs? T=1 day =8.64X 10 sec, RR=6. 106 meters Plug this in: as 034ms2(~1/300g) Close enough too that we will ignore it Storrs is a pretty good IRF Physics 121: Lecture 7, Pg 12
Physics 121: Lecture 7, Pg 12 Is Storrs a good IRF? Is Storrs accelerating? YES! Storrs is on the Earth. The Earth is rotating. What is the centripetal acceleration of Storrs? T = 1 day = 8.64 x 104 sec, R ~ RE = 6.4 x 106 meters . Plug this in: aS = .034 m/s2 ( ~ 1/300 g) Close enough to 0 that we will ignore it. Storrs is a pretty good IRF. R T 2 R R v a 2 2 S = = = 2
Newton's Second Law The acceleration of an object is directly proportional to the net force acting upon it. The constant of proportionality is the mass ∑F=F NET Units The units of force are kg m/s2=Newtons(N) The English unit of force is Pounds(lbs) Physics 121: Lecture 7, Pg 13
Physics 121: Lecture 7, Pg 13 Newton’s Second Law The acceleration of an object is directly proportional to the net force acting upon it. The constant of proportionality is the mass. F F NET ma = = Units The units of force are kg m/s2 = Newtons (N) The English unit of force is Pounds (lbs)
Lecture 7, ACT3 Newton’ s Second law A constant force is exerted on a cart that is initially at rest on an air table. The force acts for a short period of time and gives the cart a certain final speed Force Air Track For a second shot, I can apply a force only half as large(I'm getting tired). To reach the same final speed, for how long must I apply the force A)4 x as long B)2 X as long C)Same time D)1/2 as long E)1/4 X as long Physics 121: Lecture 7, Pg 14
Physics 121: Lecture 7, Pg 14 Lecture 7, ACT 3 Newton’s Second Law A constant force is exerted on a cart that is initially at rest on an air table. The force acts for a short period of time and gives the cart a certain final speed. Air Track Cart Force For a second shot, I can apply a force only half as large (I’m getting tired). To reach the same final speed, for how long must I apply the force ? A) 4 x as long B) 2 x as long C) Same time D) 1/2 as long E) 1/4 x as long