Honors Physics Unit 2

Force

an interaction between 2 object

Contact Forces

require objects to touch, ex; pushing someone on a swing

Field Forces

do not require objects to touch, ex; gravitational force (we don’t have to be touching the earth to feel its force)

Phrase for Naming a Force

The {name of force} that the {agent} exerts on the {object}

Gravitational Force

The attractive forces that objects exert on each other due to their masses (usually really small) ; earth mass (*10^ 24)

Weight =

gravitational force (weight is not synonymous with mass)

Tension Force

the force that a string/cable/cord/rope/etc exerts on an object

When is Tension Present?

whenever a rope is attached to an object and taut

Direction of Gravitational Force

force is always exerting downward on earth

Direction of Tension Force

parallel to rope, away from the object (The rope PULLS on the object) whatever direction the rope is pulling the object in

Spring/elastic Force

The force that a spring exerts on an object (only if spring is stretched or compressed (deformed)

Direction of the Spring/elastic Force

stretched springs pull, compressed springs push

Friction Force

inhibits 2 objects from sliding across one another

Static Friction

static if friction completely prevents the 2 surfaces from sliding across one another - i.e. they have the same velocity, whenever we have one object touching another and static friction is needed to keep the object(s) stationary

Kinetic Friction

if the 2 objects slide across one another - i.e. they have different velocities (surface isn’t frictionless)

Direction of Static Friction

parallel to the 2 surfaces in contact, in whichever direction needed to balance the forces ex: if you push to the right on a very heavy box but it doesn’t move, static friction is to the left to oppose your push

Direction of Kinetic Friction

opposite the velocity of the object - i.e. if a box slides to the right across the floor, kinetic friction is to the left

Air Resistance (Drag)

the force that air exerts to oppose motion of an object moving through it

Direction of Air Resistance

opposite the velocity of the object (sticking your hand out of a moving car feeling the air resistance)

Normal (applied) Force

the force that one object exerts on another by pushing on it, present anytime 2 objects are touching, perpendicular

Direction of Normal Force

perpendicular to the surfaces in contact, away from agent toward object

Vector

A quantity with magnitude and direction

what are vectors represented by

arrows

Vector Components

give the magnitude and direction of a vector according to 2 perpendicular axes

Finding Vector Components

1. Draw an x-y axis at the tail of the vector

2. Draw the x & y components- DONT FORGET ARROWS!!!

3. Use SOHCAHTOA to find the magnitude of the components

Weight =

Gravitational Force

The speed of a force=

Normal Force

Newton’s 2nd Law

Sigma Force (net force) =( mass)(acceleration)

1 Newton =

1 kg * m/s²

Balanced Force Particle Model

Fn (normal force) = Fg (gravitational force) + T_y (vertical tension)

Unbalanced Force Particle Model

T_x  (horizontal tension)  - f_k  (kinetic force) =ma (mass)(acceleration)

Fg (gravitational force) =

mg (mass)(gravitational accel. aka 9.8m/s²) 

standard acceleration due to Earth’s gravity

9.8m/s²

Equation for Kinetic Friction

(coefficient) of kinetic friction times the normal force

Equation for Static Friction

less than or equal to coefficient of static friction times the normal force

Coefficient of kinetic OR static friction

add small k or s depending on which friction