# Mechanics

#### Multimedia Resources on the Awhina website:

On Yer Bike | He Wīra Hurihuri
A spinning bicycle wheel balances like magic while dangling from a string and causes a student to spin on a rotating stool.

Faith in Physics
A heavy pendulum released from near a student’s nose will return to the same height and not quite touch her/him.

#### Other Resources:

Newton’s Third Law : “equal and opposite forces cancel” Misconception
Action-reaction forces are equal and opposite but can NEVER cancel because they are on different objects. This is widely misunderstood. This demonstration seeks to clarify Newton’s Third Law.

Newton’s Third Law: “forces aren’t equal if acceleration occurs” Misconception
Many students think that Newton’s Third Law is somehow briefly suspended when motion is initiated. This is absolutely incorrect as illustrated by this demonstration.

Newton Scales
A bathroom scale is calibrated in Newtons for proper weight measurements.

Penny and Feather in a Vacuum
A penny and a feather fall with same acceleration in a vacuum.

Beads on a string separated by quadratic distances hit the ground at equal time intervals.

Free Fall Scale
A scale attached to an object reads zero in free fall.

Newton Lifts
A student stands on a scale in a life. The scale reading increases or decreases as the life accelerates upward or downward.

Recording Student Motion
Students learn about motion and graphs by walking toward and away from a sonic ranger while observing plots of position, velocity, and acceleration.

Average Speed Puzzle – Large Version
Even though the two balls fall through the same vertical distance and have the same initial and final speeds, one ball reaches the end of its track first because it has a higher average speed.

Newton’s First Law on an Air Track
A cart moves with nearly constant velocity and the very low friction air track.

Newton’s Second Law: Acceleration of a Cart by a Hanging Mass
Cart on track accelerated by hanging mass. Data acquisition via smart pulley.

Newton’s Second Law: Cart Accelerated by a Fan
A small fan accelerates and decelerates a cart on an air track.

Fork and Spoon Balance Point
Surprising stable equilibrium point for a fork and spoon appearing to be suspended unnaturally by a match.

Tension in a String Connecting Two Masses
Tension in a string supporting a 1 kg mass, a 1 kg mass hanging over a pulley, and two 1 kg masses over two pulleys is always 10 N.

Bed of Nails
Lie down on a bed of nails and have someone smash a cinder block on your chest (really).

Suspended balls transfer momentum from one to the next.

Tennis ball on top of basketball dropped on a hard floor. The tennis ball recoils to a greater height than it was dropped from. Includes high speed video.

2D Motion on an Air Table
Puck moves in 2D, colliding with wire boundaries. Analysed with Tracker or VideoPoint. Extensive data analysis is included.

Simultaneous Fall
Two balls simultaneously dropped and projected horizontally hit the floor together because horizontal and vertical motion are independent of each other.

Collisions on an Air Table
Momentum and energy conservation during air table collisions.

Loop-the-Loop
A ball rolls down an incline and around a vertical circle only if it starts with at least a minimum height.

Rotational Inertia Wands
Students twirl equal mass wands, one with the mass at the ends and the other with the mass at the middle. The moment of inertia is found to depend on the shape.

Double Bicycle Wheel
A double bicycle wheel demonstrates addition and cancellation of angular momentum vectors: when the wheels spin in opposite directions there is no net angular momentum and the wheels can be tipped easily.

Water Rocket
The trajectory of a water rocket is studied in some detail.

Spinning Rattleback and Angular Momentum Conservation
Conservation of angular momentum is explored with the strange behaviours of the spinning rattleback by operating it on an air table. See video below.

Centripetal Force Water Parabola
Water in a spinning tank forms a parabolic surface. Explaining this in terms of centripetal force is non-trivial and very instructive.

Coupled Tuning Forks
Two matched tuning forks are mounted on resonance boxes. Hit one and the other vibrates too.