Download Newtons Laws of Motion - Instructor Outline

Instructor Outline:
Newton’s Laws of Motion
UM Physics Demo Lab 07/2013
Lab length: 80 minutes
Lab objective: To demonstrate Newton’s three laws of motion
Materials
Dedicated Components
(located in boxes):
8 Pitsco PC Sportster cars
8 sets of ½ inch x 2” steel hex bolts
with nuts
8 sets of 8 ½ inch cut steel washers
8 9” diameter round balloons
8 2” pieces of 3/8” OD-1/4” ID clear
vinyl tubing
8 3” pieces of 1/2” OD-3/8” ID black
vinyl tubing (flags to trip photo gates)
8 balloon pumps
16 spring scales 50N/5000g yellow
8 clear plastic rulers
8 sets of 6 small rubber bands
**Demonstrations:
1F20.33 Cloth from Under Dishes
1F30.u1 Frictionless Puck
1N22.20 Water Rocket
1D60.10 Relativity Cart
1N20.u1 Cannon Recoil
Beer Bottle/$20 Bill (A. Tomasch)
Model Rockets and
Engines (A. Tomasch)
Shared/Consumable Components:


1 digital gram scale


10 Pitsco 4-gram CO2 canisters
Additional rubber bands and
balloons
Guide wire/data acquisition system
for Pitsco cars: two ring stands to
support guide wire, spring-loaded
guide wire, Pitsco firing system with
12 V battery and firing button, two
photo gates, ring stand photo gate
support, aluminum roof edge guide
rails, blue masking tape to secure
guide rails to floor, laptop PC running
Logger Pro “speed trap” application
and MS Excel
Introduction: 5 minutes-Lecture
The concept of mass-inertia is reviewed and the table cloth is pulled out from under the
dishes.
Exploration stage: 10 minutes-Group lab work
Newton’s first law is investigated by observing a static car on the table top and the
straight-line motion of the air puck. The two states of motion are shown to be
compatible with zero net force by means of a simple Galilean transformation to
coordinates moving with the same speed and direction as the air puck. In the moving
coordinates the puck is again at rest and equivalent to the car sitting motionless on the
table. In both cases the motion will remain unchanged unless a net force acts.
Exploration stage: 5 minutes-Group lab work
The students next explore Newton’s Third Law by pulling on two scales connected
together to deduce that the force each scale exerts on the other is of the same
magnitude but in the opposite direction.
Property of LS&A Physics Department Demonstration Lab
Copyright 2006, The Regents of the University of Michigan, Ann Arbor, Michigan 48109
Analysis stage: 5 minutes-Lecture
Newton’s First and Third Laws are formally introduced and the results of the air puck and
scale experiments discussed. The equivalence of motion with zero net force for a
constant velocity or sitting at rest is introduced. The relativity cart demo is shown as
further illustration.
Exploration stage: 15 minutes-Group lab work
The students now construct reaction propulsion systems for the Pitsco cars from tubing,
balloons and rubber bands and demonstrate reaction propulsion by inflating the balloons
with football pumps and propelling the cars on the table top.
Analysis stage: 10 minutes-Lecture
Momentum is defined and Newton’s Second Law is formally introduced in the general
impulse-momentum form.
Exploration stage: 15 minutes-Class group activity
Each group is assigned a random number of washers (0, 2, 3, 4, 5, 6, 7, and 8) to load
onto their car. Each car is then fired down the guide wire and its final speed measured
and recorded along with its final mass.
Analysis and summary stage: 15 minutes-Lecture/Class group activity
The class data are entered into Excel and it is demonstrated that the product of the final
speed and mass of the cars is remaining constant in accordance with the impulsemomentum formulation of Newton’s Second Law J=FΔt=Δp . The constant-mass
formulation (F=ma) is then introduced. The fact that all objects fall with the same
acceleration due to gravity is explained using Newton’s Second Law and the Free Body
Diagram for a falling object. Einstein’s Equivalence Principle is mentioned to justify the
statement that inertial and gravitational mass are equivalent.
Concepts developed:
1. Mass as inertia - the resistance to being accelerated by a force.
2. Newton’s First Law of Motion - No force, no change in the state of motion.
3. Inertial reference frames and Galilean relativity: zero net force is compatible with
being at rest or in motion with a constant velocity.
4. Newton’s Third Law of Motion Action-Reaction.
5. Reaction propulsion.
6. Linear Momentum: p=mv
7. Newton’s Second Law – Impulse equals change in momentum: J=FΔt=Δp
8. Newton’s Second Law for constant mass: F=ma
9. Newton’s Second Law explains why all objects fall with the same gravitational
acceleration.
10. Equivalence of gravitational and inertial mass via Einstein’s Equivalence Principle.
Property of LS&A Physics Department Demonstration Lab
Copyright 2006, The Regents of the University of Michigan, Ann Arbor, Michigan 48109