**Hooke’s Law:**

Force due to a stretched or compressed spring.

A spring uses a proportional amount of force to turn itself back into its original state.

k = Spring stiffness

x = Displacement of the string from its starting point

**Tension:**

A force along a length of a pulling and flexible connector, like a rope and string.

**An (ideal) Pulley:**

The surface is frictionless and the wheel and rope have no real mass.

Also, only the direction of the tension force is changed, NOT the magnitude.

**Mechanical Advantage:**

Draw out all of the tension forces, that has to equal the weight of an object.

This means that if there is tension between two places, they will share the force, so the tension will be halved, which will make it easier to lift an object.

**Friction Force:**

Goes in the parallel OPPOSITE direction as the net force, and it tries to slow the object

**Kinetic Friction:**

When an object is moving, and the friction is trying to stop the object.

Fk = Kinetic Friction

uk = Coefficient of kinetic friction

N = Normal force of the object

**Static Friction:**

When objects are stationary they can also do friction.

Usually GREATER than kinetic.

This means that you can’t move an object, because the friction is so GREAT.

The “greater than” sign says that the static fraction can only increase up to a point.

This means that the MAX is when it’s EQUAL.

Fs = Static Friction

us = Coefficient of static friction

N = Normal force of the object

**Drag Force:**

When you move your hand against a fluid (gas or liquid) you are slowed down.

ALSO:

It opposes the motion of an object.

**Quadratic Drag or Turbulent Drag:**

It SCALES by velocity^2 which is why it’s called “Quadratic Drag”

Usually with LARGE objects.

C = drag coefficient

A = area of the object

p = Density of fluid

v = velocity of the object moved

**Linear Drag or Laminar Drag:**

This is used when the movement is SUPER slow.

It’s close to the one above, but velocity isn’t squared.

C = drag coefficient

A = area of the object

p = Density of fluid

v = velocity of the object moved

**Stoke’s Law:**

This represents the drag of a small sphere in a fluid.

r = radius

n = viscosity of fluid

v = velocity

**Terminal velocity:**

A point in time where the velocity becomes constant.

AKA where the Drag force is EQUAL to gravity.

**Pressure:**

Force per unit of area.

**Pascal:**

The SI unit of pressure, which is N/m^2

**Stress:**

Constant pressure on a surface.

It’s a vector.

1 female on one foot = 40 kPa

**Direct Stress:**

When the force is being directed perpendicularly/straight onto the object.

Either:

Inward: Compressive Stress

Outward: Tensile Stress

**Shear Stress:**

Force being applied parallel, like rubbing something with your elbow

**Ultimate Compressive Strength:**

How much stress a material can withstand without fracturing