Newtonian Mechanics

Vector Sum of Forces

Magnetic blackboard mechanics with spring balances and weights.

What it shows:

Solve a problem in composition of concurrent forces by graphical or trigonometric means.

How it works:

The blackboard mechanics set1 includes apparatus to demonstrate most of the common laws of statics and some dynamics. The pieces of apparatus are held on the blackboard by magnets and, although not large, are fairly visible in the lecture hall. A booklet with a few dozen suggested demonstration experiments is included in the set.
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Leaning Ladder

Small ladder against wall with variable load and inclination.

What it shows: 

A small ladder is leaned against a vertical wall. A weight can be moved up succeeding steps to find when the ladder will slip and fall down. The forces holding the ladder in equilibrium are in consideration here.

How it works: 

A short (4 foot) step-ladder leans against the wall. The reaction of the wall may be considered horizontal, tangential friction being negligible (the edge of the ladder is covered with a sheet of...

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Tension Puzzler

What It Shows

The two ends of a dial-type spring balance are each connected to strings which run over pulleys. With equal weights attached to the ends of the strings, the spring balance indicates the value of one of the weights.

How It Works

The demonstration is presented to the class as a puzzler: the spring balance is turned around so that the class can't see the dial. Students are invited to guess what it is reading. Invariably they guess the sum of the two weights. The lecturer then turns the face of the dial gauge around showing them the error of...

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Erector Spinae Muscle Forces

A realistic model of the forces in the erector spinae muscles that support the back when bent over.

What it Shows:

This is an analysis of the tensions in muscles and forces on joints as an application of torques in static equilibrium situations. The muscles involved in supporting the human torso in a stooped position are realistically modeled, and the extraordinary large forces calculated and demonstrated.

How it Works:

When bending over into a stooped position, the principal muscles which support the back are the erector...

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Irregular Lamina

center of gravity - center of mass - equilibrium

What it shows:

The center of gravity fixed in (or outside) the object always orients itself with minimum potential energy on a vertical line below the support point. When an irregular shape is thrown into the air, it is seen to rotate about its marked center of gravity or center of mass (COM).

How it works:

We have several irregular lamina to suspend and/or throw in the air. They are (1) an amoeba shaped piece of masonite pegboard, (2) a cut-out map of the U.S. glued...

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Center of Mass

Irregular lamina with marked center-of-mass tossed in air.

What it shows:

The center of gravity fixed in (or outside) the object always orients itself with minimum potential energy on a vertical line below the support point. When an irregular shape is thrown into the air, it is seen to rotate about its marked center of gravity or center of mass (COM).

How it works:

We have several irregular lamina to suspend and/or throw in the air. They are (1) an amoeba shaped piece of masonite pegboard, (2) a cut-out map of the U.S. glued...

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Shoot the Monkey

Monkey released from platform is shot by simultaneously fired cannon.

What it shows:

This is a demonstration of the independence of the horizontal and vertical components of velocity of a projectile. Often referred to as "the monkey and hunter," the problem is the following. A hunter (at ground level) aims a gun at a monkey hanging from a branch high in a tree. The monkey, being very intelligent, does not want to be shot. It knows that light travels faster than bullets and reasons that, if it lets go of the branch the instant it sees the flash of the gun,...

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High Road, Low Road

Which road is faster? A kinematics concept Puzzler.

high low road

What it shows:

Horizontal and vertical motions are independent of each other.

How it works:

Two balls, starting with the same initial horizontal velocity, take two different paths: the...

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Shoot-n-Catch

Ball shot up from PASCO cart is caught by same; a puzzler to ponder if track is tilted and cart accelerates down (or decelerates up).

shoot-n-catch

Shoot-n-Drop

Ball shot horizontally, one dropped vertically; both hit the ground at the same time.

What it shows:

The horizontal and vertical motions of a projectile are independent of each other. So two objects falling under the influence of gravity from the same height will reach the ground simultaneously, regardless of their horizontal velocities.

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Uniform Acceleration

Glider acceleration by an inclined air track or by a falling weight/string attachment; large ballbearing rolling on PASCO track (with strings).

uniform acceleration

Density

Aluminum/Uranium and SF6/Air/Helium comparisons.

What It Shows 

The concept of mass per unit volume is punctuated by having several different substances on hand for comparison. In solid materials, we have equal size chunks1 of aluminum (2.7 g/mL) and uranium (18.7 g/mL) for comparison. For gases, we typically use balloons filled with helium (0.18 g/L), air (1.29 g/L), and sulfur hexafluoride (6.50 g/L). Being 5 times heavier that air, the SF6balloon noticeably feels like it weighs more than the air-filled one and...

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