Unit 3: Force, Friction, Inclined Planes, and Torque

What is Newton's law of motion?

Fnet = ma

Fnet = net force (N)

m = mass (kg)

a = acceleration (m/s^2)

What is net force?

sum of all of the forces acting on an object

What is a free body diagram?

diagram showing all of the forces acting on an object

What is the equation for weight?

Fw = mg

Fw = weight (N)

m = mass (kg)

g = acceleration of gravity (9.8 m/s^2)

What is the force of gravity?

force acting on an object by gravity

What is normal force?

force exerted by a surface perpendicular to the surface

What is applied force?

forced applied on an object

What is the force if an object is on a horizontal surface and is not accelerating vertically?

FN = Fw

FN = normal force

Fw = weight

When does normal force not equal weight?

when there is another applied force or when there is vertical acceleration

What is normal force when there is upward acceleration?

FN = Fw + ma

FN = normal force

Fw = weight

m = mass

a = acceleration

What is normal force when there is downward acceleration?

FN = Fw - ma

FN = normal force

Fw = weight

m = mass

a = acceleration

What is net force when an object is motionless?

0

What is translational equilibrium?

when net force is 0

When does translational equilibrium apply?

when both forces up and down are equal and when both forces right and left are equal

What is true when an object is suspended from the center of a rope?

triangles with be similar

XL = XR

YL = YR

TL = TR

YL + YR = Fw

What is true when an object is not suspended from the center of a rope?

XL = XR

YL + YR = Fw

What is friction?

force that opposes motion between two objects

What is the notation for friction?

Ff

What direction is friction?

parallel to surfaces and opposite to motion

What are the two types of friction?

kinetic and static

What is kinetic friction?

friction that occurs between two objects moving within a fluid

What is static friction?

friction that occurs between two motionless objects; stronger than kinetic

What type of friction is walking?

static

What type of friction is wheels on a car?

static

How do you reduce friction?

decrease surface area, lubricants, ball bearings, smoother surfaces

How do you increase friction?

increase surface area, rough surfaces

What is terminal velocity?

greatest velocity a falling object reaches and will accelerate until Fnet = 0 and Ff = Fw

What is the symbol for coefficient of friction?

μ

What is coefficient of friction?

μ = Ff / FN

μ = coefficient of friction

Ff = friction

FN = normal force

What is the relationship between coefficient of static friction and coefficient of kinetic friction?

coefficient of static friction is greater than coefficient of kinetic friction

What is true when an object is moving on a flat plane and Fa is parallel to the surface at constant speed?

FN = Fw

a = 0

Fnet = ma = 0

Fa = Ff

What is true when an object is moving on a flat plane and Fa is parallel to the surface at changing speed?

FN = Fw

Fnet = ma = Fa - Ff

What is true when an object is moving on a flat plane and Fa is pushing down on the object at constant speed?

Fw = mg

μ = Ff / FN

Ff = Facosθ

FN = Fasinθ + Fw

Fnet = ma = 0

What is true when an object is moving on a flat plane and Fa is pushing down on the object at changing speed?

Fw = mg

μ = Ff / FN

FN = Fasinθ + Fw

Fnet = ma = Facosθ - Ff

What is true when an object is moving on a flat plane and Fa is pushing up on the object at constant speed?

Fw = mg

μ = Ff / FN

Ff = Facosθ

FN = Fw - Fasinθ

Fnet = ma = 0

What is true when an object is moving on a flat plane and Fa is pushing up on the object at changing speed?

Fw = mg

μ = Ff / FN

FN = Fw - Fasinθ

Fnet = ma = Facosθ - Ff

What is true of an object sliding downhill with no applied force at constant speed?

Fw = mg

μ = Ff / FN

FN = Fwcosθ

Fp = Fwsinθ

Fnet = ma = 0

Ff = Fp

What is true of an object sliding downhill with no applied force at changing speed?

Fw = mg

μ = Ff / FN

FN = Fwcosθ

Fp = Fwsinθ

Fnet = ma = Fp - Ff

What is true of an object sliding uphill with applied force at constant speed?

Fw = mg

μ = Ff / FN

FN = Fwcosθ

Fp = Fwsinθ

Fnet = ma = 0

Fa = Fp + Ff

What is true of an object sliding uphill with applied force at changing speed?

Fw = mg

μ = Ff / FN

FN = Fwcosθ

Fp = Fwsinθ

Fnet = ma = Fa - (Ff + Fp)