Intro to Physics How did Physics start and how does it work? Can it be captured or seen under a microscope?

Intro to Physics

How did Physics start and how does it work?

Can it be captured or seen under a microscope?

Physics is the study of the physical universe.

Some branches of Physics:a. Optics (the study of light)

b. Electromagnetism (the study of electricity and magnetism)

c. Thermodynamics (the study of heat)

d. Mechanics (the study of motion)

THIS ONE IS WHAT WE’RE STUDYING!

Though physics is definitely a branch of

, it will sometimes feel like we’re

in a class, because of all of the formulas and problem-solving.

science

math

Speed and Velocity Speed is defined as:

Rate of change of position

Velocity is simply: Speed with a direction

The defining formula for speed/velocity is:

v =dt

___

distance traveled

time interval

speed or velocity

Standard units of measure for speed/velocity:

Meters/second (m/s) But we can also use others:

km/hr miles/hr

Ex #1: A woman runs a distance of 100 meters in a time of 25 seconds. What is her speed?

4 m/s

Ex #2: A plane flies at a speed of 200km/h. How far does the plane go in 15 minutes?

50 km

Isaac Newton Though motion has been studied for thousands of years,

Isaac Newton (1643-1727) is credited with beginning physics in the way we study it now. He’s often thought of as the most influential scientist ever! (Even more important than Einstein!)

There’s a famous story that Newton saw an apple fall to the ground, and he wondered if the cause of the apple’s fall was the same reason that the moon stayed in orbit.

He tried to explain all of those motions with the idea of forces.

Forces: Push or Pull? A force can be described as a push or pull. Standard units of measure for forces:

Newtons (N). 1 N = 1kg m/s2

1 N = 0.225 lbs

There are forces acting on us all the time.

a. Gravity is pulling down on you.

b. Air pressure is pushing on us while our bodies push back.

Newton’s 3 laws of motion:

First Law:First Law: An object will continue in

its present state of motion (or rest), unless it is acted upon by a net force.

“Net force” = total of all forces acting on an object

Newton’s 3 laws of motion:

Second Law:

A net force will make an object accelerate. The size of the acceleration depends on the strength of the force and the mass of the object.

Newton’s 3 laws of motion:Third Law:Third Law:

For every action force, there is an equal and opposite reaction force.

Newton’s 1st Law (Revisited): The easy example: An object sitting still

will only start moving if…

A net force makes it start moving

Newton’s 1st Law (Revisited): The more difficult example: An object in

motion will only change its motion if… A net force makes it speed up or slow down.

So why do most objects seem like they have a natural tendency to slow down and stop? Friction provides a net force, which stops the

object.

Newton’s 1st Law (Revisited): Newton’s 1st Law is sometimes known as

the law of inertia. Inertia is defined as the tendency of objects

to continue their motion, and mass is a measure of an object’s inertia

Newton’s 1st Law (Revisited): Ex #3: Correct the following statement: An

object will only move if a net force acts on it.

An object will only accelerate (or change motion) if a net force acts on it.

Ex #4: Two forces are pulling on an object in opposite directions, as shown in the diagram. The object is at rest and is continuing to stay at rest. Find the size of F2 if F1 = 300N.

F2 = ?F1 = 300N

Ex #4: Answer:

Because the object is at rest, there must be zero net force on the object.

So F2 must also equal 300N, for the net force to equal zero.

F2 = 300NF1 = 300N