Physics - Unit 1b: Newton's Laws (Forces)

Semester #1 review deck for midterms

What is the 1st Law?

The law of inertia

What is the deal with the 1st law?

The 1st law (the law of inertia) deals with no change in motion; how objects react to being pushed or pulled and how difficult it is (or not) to change the motion. It deals with objects either at rest or in constant motion and the forces at work are balanced.

What is the deal with the 2nd Law?

The 2nd law (F_net = ma) deals with the relationship between acceleration (change in motion), net force (the cause of the change), and mass (the natural resistance to change). It deals with objects that are being accelerated and the forces at work are unbalanced.

What is the deal with the 3rd law?

The 3rd law (action/reaction) deals with force as an interaction between two objects and the fact that the two objects actually hit each other with equal force.

What is force?

A push or a pull

What are the two types of forces?

contact forces and field forces

Force is a…

vector

In the metric system, what unit do we use?

Newtons

What unit do we use with the imperial (english) system?

pounds

What is the definition of inertia?

Inertia is the resistance to change and is measured by the mass of the object in kilograms (kg).

Force =

push (cause)

inertia (mass) =

push back (resistance)

Acceleration =

change in motion (outcome of push vs. push back)

Newton’s 1st Law

An object at rest will remain at rest, and an object in motion will stay in constant motion UNLESS acted upon by an outside net force.  

With the 1st law, objects will either be…

at rest or a state of constant motion

Net force

 The sum of all forces acting on an object. When multiple forces act on an object, the net force is the cumulative/overall effect of all forces present, or, if you replaced all of the forces with just one force, the object would still behave (move or not move) in the same manner.

The outcome of the first law

zero net force

zero net force

the forces are balances, or that they are equal but opposite and therefore cancel or zero out and the motion of the object will not change

zero net force = balanced forces =

no change in motion

With the 1st law, an object at rest will…

remain at rest (no change in motion)

with the 1st law, an object in motion will remain…

in constant motion (no change in motion)

Definition of friction

A naturally occurring force that opposes all motion and applied forces

Types of friction

Static friction and kinetic friction

Static friction

Friction is at rest. It is the stronger of the two

Kinetic Friction

The friction of change. The object must be moving ot use this friction

Net force doubled =

the acceleration is also doubled

Any change in the net force will result in the exact same change in the acceleration AS LONG AS

the force stays constant

the 2nd lAW is a law of…

acceleration/change in motion

In the 2nd law, the objects will either

speed up or slow down

Unbalances forces means

there is a net force, which mens the object is acceleration in the direction of the net force

acceleration is directly proportional to…

net force

acceleration is inversely proportional to…

mass

Newton’s 2nd law of motion

Fnet=ma

Net force = mass x acceleration

Fnet=ma

Newton’s 1st and 2nd laws have this in common:

they isolate one object, identify the forces acting on his, determine if there is a net force on the object or not then calculate any acceeration that may be present

Newton’s 3erd law:

“for every action there is an equal and opposite reaction”

The 2nd law says that

The forces exchanged by the two objects must be equal, but because force involves both mass and acceleration

Fores must be equal…

but the acceleration that two collided objects created are usually not

F_A = F_B equals

m_Aa_A = m_Ba_B

the 3rd law means…

The force is happening in pairs of objects, and there will be an object slowing down and speeding up with acceleration. 

Can we see the force?

No, we only see the acceleration occurring when two object collide