Do Now:
1.
2.
3.
4.
Walk in silently.
Grab a calculator and any papers for today.
Grab 1 chromebook per pair.
Silently practice your vocab.
Due Next Class:
•
Finished IP/HW
By the end of today, IWBAT…
explain periodic motion of a pendulum
and calculate the length of a
pendulum, and determine the spring
constant using Hooke’s Law.
Why it matters in LIFE:
Part of being a
functional human
being is being able to
understand what’s
happening in the world
around you!
Why it matters in THIS CLASS:
Our Goal = 80%
Mastering today’s lesson (focused
participation, asking questions, etc)
is the first brick that will help us
reach our goal for this unit, and
eventually for the year
TEKS:
(B) investigate and analyze
characteristics of waves, including
velocity, frequency, amplitude, and
wavelength, and calculate using the
relationship between wavespeed,
frequency, and wavelength;
By the end of today, IWBAT…
explain periodic motion of a
pendulum and calculate the
length of a pendulum, and
determine the spring constant
using Hooke’s Law.
Topic:
Periodic Motion
https://vimeo.com/804917
59
PERIODIC MOTION
-The back and forth movement of an object between
two opposing points.
is called Periodic Motion:
 If the motion repeats
 If the motion follows the same path in the same amount of time
We refer to these repeating units of periodic motion as cycles.
Period, T (s) is the time it takes to complete one cycle.
SIMPLE PENDULUMS
Click for
Simulation
We saw that the period of a pendulum, T
 Depends on the length, l, of the pendulum
 Depends on the gravitational constant, g
 Does not depend on the mass of the bob
 Does not officially depend on the amplitude, θ, of oscillation
 Unofficially, it does, but the effect is too small to count, so we ignore this
dependency for our class
𝑙
𝑇 = 2𝜋
𝑔
T = period (s)
l = length of the pendulum (m)
g = acceleration due to gravity (m/s2)
EXAMPLE
A grandfather cat has a period of 1 second.
Determine the length of the pendulum.
EXAMPLE
A grandfather cat has a period of 1 second.
Determine the length of the pendulum.
GP #1
VOCAB CARDS
LIGHTNING
ROUND!
SPRINGS
Springs can also cause periodic motion!
The stretching and compressing of a spring is
periodic when it is consistent and repetitive.
Spring constant, k, (units N/m)
Measures the stiffness of a spring.
A larger k value spring takes more force to stretch!
SPRINGS & HOOKE’S LAW
F = -kx
F = Force exerted by the spring (N)
k= spring constant (N/m)
x = distance the spring is stretched or compressed
from equilibrium
The period of a mass on a spring can also be calculated and it:
 Depends on the mass, m, attached to the spring
 Depends on the spring constant, k, of the spring
The period of a mass on a spring can be calculated by the
following formula:
𝑇𝑠𝑝𝑟𝑖𝑛𝑔
𝑚
= 2𝜋
𝑘
Tspring = period of the spring (s)
m = mass (kg)
k = spring constant (N/m)
EXAMPLE
A spring stretches by 18 cm when a bag of potatoes
weighing 56 N is suspended from its end.
a) Determine the spring constant, k
b) Determine the period.
INDEPENDENT PRACTICE!
Procedure for IP time:
1)
Silent work time
2) Try and solve without notes first!
Hierarchy of who to ask
1) Your brain
2) Your notes
3) Ms. Kelly (after you #embracethestruggle)
EXIT TICKET
A bag with a weight of 20N hangs from a spring with a k of
10 N/m .
a) How far does it stretch?
b) What is its period?
EXIT TICKET
A bag with a weight of 20N hangs from a spring with a k of
10 N/m .
a) How far does it stretch? 2m down, (-2m)
b) What is its period? 2.84 s