Section 1

Force + Newton’s 1st Law

Basis of mechanics:

Newtons 3 laws of motion + law of universal gravitation

A push or pull on a body

Force

Force causes:

1. Distortion in body
2. Change in body’s velocity
3. Both

Force is a … quantity

Vector

Units of Force:

Metric:


1. Newton (N)
2. Dyne
3. Metric ton (2000 N)

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English:


1. Pound (lb)
2. Ounce (oz)
3. Ton (2000 lb)

Force of gravity acting on a body

Weight (W)

Direction of weight is … & weight depends on …

1. ALWAYS toward the earth’s center
2. Which planet you’re on

Weight acts in which object:

1. Stationary
2. Moving vertically
3. Moving horizontally

Force of resistance to relative motion between 2 bodies or substances in physical contact

Friction

What exists between (tire & road) or (car & air)?

Friction

Types of Friction:

1. Static
2. Kinetic

Resistance when u try to start sledding an object

Static Friction - No relative motion between surfaces.

Resistance while sliding an object

Kinetic Friction - relative motion

Which is stronger Kinetic or static friction?

Static > Kinetic

Object will remain at rest or in motion with constant velocity, unless acted on by a net external force

Newtons First Law of motion

Force applied to the object from some other object

External Force

( Ex: force first impact, gravity, air resistance )

Vector sun of ALL external Forces

Net force

Net Force Cases:

A) push opposite ends w/same force

B) Push same direction

C) Push in different directions

A) Net force = 0 (cancel)

B) Net force is non-zero

C) Net force: “in-between” direction

Key concept of Newtonian mechanics

Force

The agent for a change in motion

Force

Newton’s 2nd law is important for …

Applying mechanics in the real world

An object is accelerated when a net external force acts on it

Newton’s 2nd law of motion

Net force formula

F = ma

• a=F/m

F & an are … relationship & both …

• Direct

• Vectors

Direction if object’s acceleration & net force

Same

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(Direction of a & F is the same)

Units in Net force formula:

F: N

a: m/s^2

m: kg

\
1N = 1 kg • m / s^2

What keeps car on road?

Friction between the road and tires

• if road to slick, tires can’t grip, and you peel l-out

Which Law establishes the relationship between mass & weight

Newton’s 2nd law of motion

Acceleration of object falling due to Earths gravity

g= 9.8m/s^2

Force an object feels from Earth & formula

Weight (W=mg)