Bernoulli Balls

Bernoulli Balls

A simple hair-dryer becomes a magical levitation device through an understanding of the principles of fluid flow.

Ingredients:

1. hair dryer (make sure you have an appropriate power supply available!)
2. small light balls (such as polystyrene balls available at most craft shops, or ping pong balls)

Instructions

1. Orient the hair dryer so that the outlet is pointing directly upwards. Turn it on.
Place a ball carefully in the flow from the hairdryer. It will balance in the air, appearing to levitate!
2. Gently move the hairdryer from side to side – the ball will stay in the air stream, i.e. will also move back and forth. Repeat this process moving the hairdryer up and down.
3. Carefully tilt the hairdryer – the ball will still stay in the airstream, hanging in mid-air with nothing directly underneath it.
4. Try using balls of differing sizes, and challenge your audience to see how many they can place in the airstream at once.

How Does it Work?

The upward pressure from the hairdryer balances the downward force of gravity, keeping the ball 'levitating'. The more impressive part of this trick is being able to move the ball along with the hairdryer and angle it. The stream of air sticks to the surface of the ball. This is a demonstration of the Coanda Effect, which emerges when fluids like air or water pass over curved surfaces. When the ball approaches the edge of the stream, air is curved round the ball and directed out of the stream. This has the effect of pushing the ball back into the stream. This is the process that enables the ball to balance inside the airstream and stay in the airstream as the hairdryer is moved around.

Tips for Success

Try to find a hairdryer with a 'cool' setting – it will last longer and allow you to perform the trick for much longer in one sitting, without the hairdryer overheating. Make sure that the balls aren't larger than the output of the hairdryer or it won't work. Tilting the hairdryer to too great an angle will cause the ball to fall out of the airstream – although most audiences enjoy seeing the effect!

Serving Suggestions

This is a good eye-catching demonstration that can keep audiences amused for a significant period of time – everyone wants to have a go, especially when challenged to make the largest number of balls stay within the airstream. However, it does require a power supply so is generally limited to indoor venues.

Did You Know?

The Bernoulli Effect underlies the principle of the aerofoil. By encouraging air to flow more quickly over the top surface of a wing an upward pressure is produced by the slower moving air beneath. This phenomenon can also be demonstrated by holding up two sheets of paper and blowing between them. Instead of moving apart, they are drawn together. If you thought anyone could have worked this out, remember that Daniel Bernoulli was awarded his masters degree at the ripe old age of 16.

Source:-
http://www.physics.org/interact/physics-to-go/bernoulli-balls/index.html

Balloon Kebabs

Balloon Kebabs

Density and pressure effects are explored using a simple visual demonstration.

Ingredients:

balloons
wooden kebab skewers

Instructions

1. Blow up the balloons (not full) and tie them off.
2. Challenge your audience to make a 'balloon kebab' – to insert the wooden skewer all the way through the balloon without popping it. Let a few people have a try – they will invariably try to insert the skewer fairly slowly through the side, and the balloon will pop.

Show them how physics can make the trick work:

1. Start by lining up the skewer point with the darker patch on the balloon, opposite the tie end. Gently push the skewer through. You may find that a twisting motion works best.
2. Once the skewer is through one side, push it gently through the balloon until the point of the skewer is at the opposite end – the darker area around the tie.
3. Insert the skewer tip gently through the soft part of the balloon where the tie is – again use the twisting motion if it helps. Voila! – you have made a balloon kebab!

See video at:- http://m.youtube.com/watch?v=jwE4oSv7Qds

How Does it Work?

This trick works through an understanding of surface properties. A balloon is formed by inserting air into a flexible thin rubber sheet. Most of the balloon is stretched evenly, but there are two points where the rubber is least stretched – and thus there is the lowest surface tension. These correspond to the tied section and the darker patch at the opposite side of the balloon – in fact the darker colour indicates that the balloon is less stretched over that region. Most of the balloon is under high tension, so attempting to push the skewer through just makes the balloon pop. But at the low tension sections it is possible to make a small hole without breaking the overall surface of the balloon.

Tips for Success

This trick works best with round balloons (rather than long skinny ones) – mainly so that the kebab skewers can fit! Don't blow up the balloon too much or it will pop even if you do it correctly. Make sure the skewer ends are fairly sharp – blunt skewers are more likely to pop the balloon.
You may find that your balloons sometimes burst even if you follow the instructions. The audience will enjoy the entertainment so just laugh it off and try again!

Source:- http://www.physics.org/interact/physics-to-go/balloon-kebabs/index.html

Is this anti-gravity wheel a magic trick or just cool physics?

A man effortlessly lifts a 42-pound weight at the end of a long rod over his head. It seems like it's floating! What is this sorcery? Is this guy a wizard? Perhaps he has discovered an anti-gravity device to make Back to the Future skateboards? Actually, it's just good old physics in action.

First watch the demonstration by Veritasium's Derek Muller:

http://m.youtube.com/watch?t=36&v=GeyDf4ooPdo

The phenomenon that makes this seemingly magical act possible is called torque-induced precession—also known as gyroscopic precession:

Torque-induced precession is the phenomenon in which the axis of a spinning object (e.g., a part of a gyroscope) "wobbles" when a torque is applied to it, which causes a distribution of force around the acted axis. The phenomenon is commonly seen in a spinning toy top, but all rotating objects can undergo precession. If the speed of the rotation and the magnitude of the torque are constant, the axis will describe a cone, its movement at any instant being at right angles to the direction of the torque. In the case of a toy top, its weight is acting downwards from its centre of mass and the normal force (reaction) of the ground pushing up on it at the point of contact with the support constitute two opposite and equal forces producing a torque.
The phenomenon doesn't make the weight lighter, although it will feel lighter to person lifting it.

Still not clear about how it works?

Here's the video that explains it all in detail:

http://m.youtube.com/watch?v=NeXIV-wMVUk&t=12

Source:-
http://sploid.gizmodo.com/is-this-anti-gravity-wheel-a-magic-trick-or-just-cool-p-1546185172

<script data-ad-client="ca-pub-5661085866627725" async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>

WATERPROOF HANKY

A great excuse to threaten to pour water over your audience – but with a surprise twist thanks to physics.

Ingredients:

large glass
ashtray or similar
water
handkerchief

Instructions

Push the centre of the handkerchief into the glass, so that the edges are hanging over the outside of the rim of the glass.
Pour water into the glass, through the loose handkerchief. Make sure that your audience can see the water easily passing through the handkerchief into the glass. Keep pouring the water until the glass is roughly half full.
Pull the corners of the handkerchief so that the material is taut over the top of the glass. Hold the glass and handkerchief so that the material stays tightly stretched over the opening. For younger audiences you may like to say some 'magic words' that make the hanky waterproof.
Place the ashtray on the top of the glass and tip it all upside down, being careful to keep the handkerchief pulled tight.
Choose a likely suspect from your audience to threaten with a drenching! Hold the upside-down glass and ashtray above their head, making sure that the glass is vertical and the handkerchief is tight. Remove the ashtray and voila! – nothing happens! The water stays inside the glass.
How Does it Work?

This demonstration is based on surface tension and air pressure. When the handkerchief is loose, the water can pour through the gaps in the fabric. However, when the handkerchief is pulled tight, the water molecules can form a single surface or membrane across the handkerchief due to a property called surface tension. The air surrounding us is exerting a force in all directions - air pressure. When the membrane is formed on the surface of the handkerchief, it provides a uniform surface for the air pressure to act upon. The force of the surrounding air acting upon this membrane is sufficient to overcome gravity, and so the water stays in the glass.

Tips for Success

Don't try to substitute a paper tissue for the handkerchief as it won't work! If the glass isn't held vertically, some water may dribble out where the membrane attaches to the edge of the glass.
Serving Suggestions

This trick will work in almost any environment and with any age group.

Did You Know?

Galileo was among the earliest to demonstrate the existence of surface tension on water by showing that an iron needle can be floated lengthways on water, but not on its point.

Source and See video at:- http://www.physics.org/interact/physics-to-go/waterproof-hanky/index.html

How to break the bottom of a bottle without turning it into smithereens

How to break the bottom of a bottle without turning it into smithereens

Fill an empty beer bottle with water, leaving a small gap at the top. Then firmly hold the bottle by the neck and hit its top with your other hand.

What happens:

The hits create a shock wave of pressure, which breaks the bottom of the bottle exactly at that point, without the slightest damage to the remaining bottle.