Newton’s Second Law

1. Newton’s Second Law Level 1 Physics

2. Newton’s Second Law (N.S.L.) When a net external force (SF) acts on an object of mass m, the acceleration a that results is directly proportional to the net force and has a magnitude that is inversely proportional to the mass. The direction of the acceleration is the same as the direction of the net force If the force increase, then acceleration will also increase. If the mass increase, the acceleration will decrease.

3. N.S.L. Now Double the Force A 100 N force will produce an acceleration of 2 m/s/s on a 50 kg mass. A 200 N force will now produce an acceleration of 4 m/s/s on the same 50 kg mass.

4. Example 3 N 10 N 10 kg Magnitude of FNET= Direction = Acceleration = 7 N RIGHT 0.70 m/s/s

5. Starting Guide Draw a free body diagram Break vectors into components if needed Find the NET force by adding and subtracting forces that are on the same axis as the acceleration. Set net force equal to “ma” this is called writing an EQUATION OF MOTION.

6. Example An elevator with a mass of 2000 kg rises with an acceleration of 1.0 m/s/s. What is the tension in the supporting cable? Equation of Motion T mg 21,600 N

7. Example A 50 N applied force drags an 8.16 kg log to the right across a horizontal surface. What is the acceleration of the log if the force of friction is 40.0 N? Fn a 50 N 40 N mg 1.23 m/s/s

8. Example A sled is being accelerated to the right at a rate of 1.5 m/s/s by a rope at a 33 degree angle above the + x . Calculate the Frictional Force if the mass of the sled is 66 kg and the tension in the rope is 150 N. FN T Tsinq q Tcosq Ff mg 26.8 N

9. A Final Note