Mechanics 1 Flashcards
Dynamics
the explanation of motion in terms of forces that act on an object
Force
push or pull exterted by one object on another
Summary of Forces
If you pull on a rope attached to a crate, you create a tension in the rope that pulls the crate. When a sky driver is falling through the air, the earth exerts a downward foice called the gravitational force and the air exerts an upward force called air resistance. When you stand on the floor, the floor provides an upward, supporting force called the normal force. If u slide na book across the table, the table exerts a frictional force against the book so the book slows down and eventually stops. Static cling provides an example of the elctrostatic force. (All the forces mentioned above with the exception of gravity are ultamitely due to electromagnetic forces).
Newton’s First Law
An objects state of motion - its velocity - will not change unless a net force acts on the object.That is if no net force acts on an object, thenif the object is at rest, it will remain at restand if the object is moving, then it will continue to move with constant velocity (constant speed in a straight line)no net force = no acceleration
Inertia
property of objects that describes their natural resistance to change in their state of motion. The first law is ofeten referred to as the law of inertia
The first law applies that there is no NET force on an object so that means….
could mean that there are no forces at all but more commonly it means that the forces on an object balance out (total of all the forces in each dimension is zero)
The mass of an object is the quantitive measure of its ________
inertia (mass measures how much matter is contained in an object) Mass is measured in kilograms
Newtons second law
If Fnet is the net or total foece acting on an object of mass m then the resulting acceleration of the object, a satisfies this simple equationFnet = ma
Notice that the first law is really just a special case of
the second law, the case in which Fnet = 0
Forces are represented by ________ because a force has a __________ and a ___________
forces are represented by vectors because force has a magnitude and direction
Net force is simply
the sum all individual forces
Fnet is the sum of all the forces that act on the object namely the object whose mass, m, is on the other side of the equation. Any force exerted by the object is not included in Fnet
(How well do u understand this?)
Because mass is a positive number, the direction of acceleration is always the same as the direction of Fnet ……
Therefore an object will accelerate in the direction of the net force it feel, this does not mean that an object will always move in the direction of Fnet .
What if Fnet = 0? Then a = 0. What does a = 0 mean?
It means that the objects velocity does not change, which is also what Newtons first law says.
Does Fnet = 0 mean that v = 0?
NO!!!!! , Fnet = 0 means that an object will not accelerate not that it wont move (VERY IMPORTANT)
Fnet = ma is a vector equations so it automatically means that the components of both sides must be the same. In other words, Fnet could be written as the sum of a force in the horizontal direction plus vertical direction
(Do u understand this)
What is the unit of force?
Its the unit of mass * the unit of accelerationForce = [m] [a] = kg * m/s2A force of kg * m/s2 is called 1 newton (N).1 N = 1/4 of a pound.
Newtons 3rd Law
If object 1 exerts a force, F 1-on 2, on object 2, object 2 will also ecert a force F 2-on-1 . These 2 forces will have the same magnitude in opposite directions (they act on different objects). The 2 forces are said to form an action reaction pair.Note: does not say that the effects of these forced will be the same (different for diff masses)
Newtons 1st law vs Newtons 3rd Law
1st law: all forces must be acting on a single object, net force = sum of vectors3rd law: each force must be acting on a different object in action reaction pair
Newtons 3rd law confusing concepts
1) just because 2 forces are = and oppisire doe snot mean they form an action reaction pair, forces also have to be from 2 objects acting on each other2) 3rd law will apply when objects experience acceleration, 1 object accelerates other one will push back
What to do when calculating forces exerted on 2 diff objects
remember that its opposite, lets say M = 100 and m = 50 and a = 2, the force exerted by the larger crate on the small one is 50 * 2 = 100 N, smaller crate on larger one is 100 * 2 = 200 N
Mass
intrinsic property of an object and does not change with location
Weight
The weight of an object is the gravatational force exerted on it by the earthweight is a force so we can use f=ma to compute, setting a = gwe get w = mg
Newton’s law of Gravitiation
Every object in the universe exerts a gravitational pull on every other object. The magnitude of this gravitational force is proportional to the objects masses and inversely proportional to the sqaure of the disrance between them
