The English physicist Isaac Newton (1642-1727) was one of the greatest physicists of all time. His conception of the universe, which he formulated at age 24, lasted for almost 300 years until the end of the 19 th century when other scientists began finding holes in his theories.
Also called the Law of Inertia An object in motion (or at rest) tends to stay in motion (or at rest) unless acted upon by an external force.
Translation of Newton s First Law for the Hood : Getting up is hard to do but once your are out and about it is easy to keep going Likewise, if you are in your ride without a seatbelt and you slam into a wall your car will stop but you will just keep on going. Driver without seat belt just keeps on moving
P.O.D. 1: Newton s First Law. 1. TRUE OR FALSE. Headrests on car seats stop whiplash from happening which occurs when a car gets hit from behind. Whiplash is a consequence of Newton s First Law. 2. Suppose you put a ball in the middle of a wagon and accelerate the wagon to the right. A. What will the ball appear to do to someone standing on the ground right to the side of the wagon? B. What will the ball appear to do to someone in the wagon with the ball? 3. How does a bull fighter use Newton s First Law to save his life?
The acceleration of an object is directly proportional to the force applied to it a F and inversely proportional to its mass. a 1 m
The hanging weight applies a force (F) to the mass cart (m) making it accelerate (a) according to F = ma
Suppose we double the weight of the hanging metal. What happens to the acceleration of the cart? 2 If the force doubles 2 2 the acceleration doubles.
Who is applying more force?
Who is applying more force?
All other things being equal, who is applying more force?
Suppose we double the mass of the mass cart. What happens to the acceleration of the cart? 2 1 2 1 2 If the mass doubles the acceleration halves.
All other things being equal, who will accelerate faster?
All other things being equal, who will accelerate faster?
P.O.D. 2: What happens to the acceleration of the space shuttle as it goes higher and higher? a. Gets bigger b. Gets smaller c. Stays the same Why?
Review of the forces we deal with F w = force of weight F w = m g (weight equals mass gravity) F w
Review of the forces we deal with F N = normal force F N = F W (in a simple equilibrium situation on a flat surface) F N F w
Review of the forces we deal with F p = pushing/pulling force F x = F p cos F y = F p sin F x F P F w F N F y
Review of the forces we deal with F f = frictional force F f = F N (where is the coefficient of friction and is a constant) F x F P F w F N F y FF
Review of the forces we deal with F T = force of Tension F T F x F P F w F N F y FF
P.O.D. 3: Draw (with arrows) and Label (F w, F N, F f, F p, F bouy, etc.) 5 of the forces acting ON the boat below.
For every action there is an equal and opposite reaction.
Force of Gun on Bullet vs. Recoil of Bullet on Gun Force of Fist on Face vs. Force of Face on Fist Force of Runner on Girl vs. Force of Girl on Runner Force of Balloon on Face vs. Force of Face on Balloon Force of Man on Pants vs. Force of Pants on Man
The two forces shown form an action/reaction pair Pay attention to the prepositions Gloves protect the other boxer s face but also the gloved boxer s hand.
Newton s Third Law: F 2 = F 1 F 2 = force of red jerseyed football player on orange jerseyed football player F 1 = force of orange jerseyed football player on red jerseyed football player F2 F1 If F 1 = F 2, how come the results are not the same on both players? In simplest terms, it is because the player on the left has more mass than the player on the right and so the player on the right must undergo a greater acceleration than the player on the left. F 2 = F 1 M a = m a
The boxer s head has a small mass, therefore, it undergoes a big acceleration The boxer s arm, shoulder, and torso have a big mass, therefore they undergoes a small deceleration
If the action and reaction forces are equal and opposite, why don t they cancel each other out? Canoe pushes on boy s feet with a Force F 1 This causes the boy to move forwards. Boy pushes on canoe bottom with Force F 1 This causes the boat to move backwards.
P.O.D. 4: A big truck crashes into a small car. a.which has a greater mass? b.which exerts the greater force on which? c.which undergoes the greater change in velocity (acceleration/deceleration)?