Transcript laundry basket

Forces On An
Inclined Plane
Think about the forces as she sleds
down the hill in the laundry basket (if it
is not a non-frictionless surface). Can
you label them?
FN
30°
What is the formula used to
calculate Fg?
How many other forces are
there? (Don’t make any up!)
Two; the normal force (FN)
and the force of friction
(Ff).
Fg = mg
The force due to gravity can be broken
up into vectors using the tip to tail
method. They are Fgll and Fg┴.
Fgll = Fgsin θ
The formulas used to
calculate the components
are:
30°
Fg
Fg┴ = Fgcos θ
One way to remember when to use cosine or sine is to look at the formulas on your reference
table. Ax = A cos θ (horizontal) and Ay = A sin θ (vertical). Just use the opposite function for that
direction when on an incline. Fg┴ = Fgcos θ (vertical) and Fgll = Fgsin θ (horizontal).
• Other formulas you need to know:
–Ff = μFN (μ = coefficient of friction)
–ΣFx = Fnet = ma = Fgll – Ff (ΣFx = sum
of the forces in the x- direction)
Example:
If a 60 kg person is sledding down a hill on
waxed skis (yes, it’s a laundry basket, but
just pretend!) at a 30o incline at a constant
velocity, calculate Fnet, FN, Fgll, Fg┴ , Fg, and Ff.
The easiest thing to find first
is the weight (Fg).
Fg= mg
Fg= (60kg)(9.81m/s2)
Fg= 588.6N
Fgll = 294.3N
Use the weight to find it’s
vectors.
30°
Fg┴ = 509.73N
Fg┴ = Fgcos θ
Fg┴ = (588.6N)cos(30°)
Fg┴ = (588.6N)(0.866)
Fg┴ = 509.73N
Fgll = Fgsin θ
Fgll = (588.6N)sin(30°)
Fgll = (588.6N)(0.500)
Fgll = 294.3N
Fg = 588.6N
What is the normal force equal to?
(Remember, it has to be equal and opposite
of another force.)
It is equal to Fg┴. The normal force is pushing down
with 509.73N of force while the ground is pushing up
with an equal amount of force.
FN = 509.73N
To find the force of friction, plug in the normal force and
the coefficient of friction that says waxed ski on snow.
Fgll
This would be ________
kinetic
friction because it is SLIDING.
Ff = μFN
Ff = (0.05)(509.73N)
Ff = 25.49N
30°
Fg
*Since coefficients of friction don’t
have units, keep the unit of a Newton.*
Fg┴
The last thing to figure out with all of
the forces is the net force.
Since she is going down the hill at a
constant velocity, what does that
mean?
***ZERO acceleration.***
Keep that in mind!
0
ΣFx = Fnet = ma = Fgll – Ff
Fnet = Fgll – Ff
Fnet = 294.3N – 25.49N
Fnet = 268.81N
Fgll = 294.3N
30°
Subtract the force of friction because it
is in the opposite direction of motion.