1 Newton’s Laws

2 1 st Law – Inertia Newton's first law of motion is often stated as: An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. unless acted upon by an unbalanced force

3 2 nd Law Newton's second law of motion can be formally stated as follows: The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. In terms of an equation, the net force is equated to the product of the mass times the acceleration. Fnet = m a

4 3 rd Law "For every action, there is an equal and opposite reaction."

5 1 st law restated Inertia - the tendency of an object to resist a change in its motion –If at rest, wants to stay at rest –If moving, wants to continue moving –UNLESS ACTED UPON BY AN OUTSIDE FORCE! – Class/newtlaws/u2l2b.htmlhttp:// Class/newtlaws/u2l2b.html

6 Inertia and mass are related in that the more massive an object is the more resistance to change in the object’s motion or INERTIA

7 Assignments On Slide 8 do: 1-6 On Slides do: 1-9, 12, (odds only), 36. Show formulae, work with numbers and units, and answers with numbers and units for odds.

8

9

10

11

12

13

14 There are many more applications of Newton's first law of motion. Several applications are listed below – try to provide explanations for each application. blood rushes from your head to your feet when riding on a descending elevator which suddenly stops.

15 the head of a hammer can be tightened onto the wooden handle by banging the bottom of the handle against a hard surface.

16  a brick is painlessly broken over the chest of a physics teacher by slamming the brick with a sledge hammer. (CAUTION: Do not attempt this at home!)

17  to dislodge ketchup from the bottom of a ketchup bottle, the bottle is often turned upside down, thrust downward at a high speed and then abruptly halted.

18  headrests are placed in cars to prevent whiplash injuries during rear-end collisions.

19  while riding a skateboard (or wagon or bicycle), you fly forward off the board when hitting a curb, a rock or another object which abruptly halts the motion of the skateboard.

20 2 nd Law (F=ma)

21 F m a Force, F units: newtons 2 nd Law Mass, m kg Acceleration, a m/s 2 Problem: Find the net force necessary for a l.6 x 10 3 kg car to accelerate forward at 2.0 m/s 2. F = ma = 1.6 x 10 3 kg (2.0 m/s 2 ) F = 3.2 x 10 3 kgm/s 2 or newton, n

22 Weight = mass x free fall acceleration W = mg On Earth, g = 9.8 m/s 2 A 1.0 kg object has a weight of l.0 kg x 9.8 m/s 2 = 9.8 n If you weigh 125 lb, find your weight in newtons. 125 lb 1 kg 9.8 m = n 2.2 lb s 2 What law is this? w m g

23 3 rd Law For every action force There is an equal and opposite reaction force.

24 ETC. Centripetal Force - the force that pulls an object moving in a circle toward the center of the circle. Object moving clockwise in a circle is always being pulled toward the center of the circle and 2. show centripetal force vectors.

25 Kinetic and Potential Energies Kinetic Energy - energy of motion Potential Energy - energy of position KE = max PE = 0 KE = 0 PE = max KE = 0 PE = max

26 KE and PE KE = ½ m v 2 Kgm 2 = joule or j v 2 PE = mgh Kg m m = joule also s 2 g = 9.8 m/s 2

Universal Forces Electromagnetic Forces - act between charged particles –Opposites attract for both electric and magnetic forces –Electric force is responsible for repulsion of like charged particles Nuclear Forces –Strong nuclear force holds neutrons and protons together in the nucleus –Weak nuclear force (weaker than the strong n.f.) acts only over very small distances and is involved in nuclear decay Gravitational - acts between any two objects in the universe and acts over large distances