A
Complete Guide to
Horses Forces
Teachers’ Notes Key Stage 3
INTRODUCTION
Quantum Theatre for Science is Britain’s foremost
Theatre-in-Education Company currently performing to nearly 7% of all Primary
aged children in England and Wales and this year, in partnership with
Rolls-Royce, Quantum is returning to the Secondary sector, with a brand new
play on forces.
Founded 12 years ago in response to a lack of provision of
drama in the science sector Quantum now has plays covering all aspects of the
science curriculum, all written and performed in its own particular style,
providing a highly original and entertaining teaching tool for the introduction
and revision of the topics listed in the National Curriculum for Science.
Our latest play, A Complete Guide to Horses Forces,
aims to introduce and explain the sections on Forces for Key Stage 3 children,
from the basic types of forces (pushes, pulls etc.) through Gravity and Newtons
to inertia, turning forces, floating and sinking and pressure.
The material is presented in a Cabaret style, with various
songs, sketches and historical vignettes illustrating the scientific concepts
explored as we follow the fortunes of the two presenters who battle through
interruptions, obstacles and real life drama in their attempts to present A Complete Guide to Horses Forces.
THE FORCE OF GRAVITY
With Sir Isaac Newton as our guide we explore the nature of
Gravity as a pulling force between all objects.
The idea of Gravity as a pulling force between all objects
is introduced. Sir Isaac tells us that
between any two objects there is a force of attraction and he and Diamond (his
pet dog) try holding out two apples to see if they pull each other
together. He explains that the pulling
force between the apples is too small for us to see due to the fact that the
apples are so small. Sir Isaac then
lets one apple go and we see the effect of the pulling force of the Earth on
the apple as it falls to the ground. We
draw the conclusion that the Earth’s pulling force is big enough to notice because
of the vast size of the Earth relative to our apple.
Galileo’s experiment of dropping two objects of differing
weights from a height is set up and we see that the objects fall at the same
rate. We conclude that the force of
Gravity is a constant producing uniform acceleration.
Finally Sir Isaac measures Gravity in Newtons using a
Newtonmeter. By weighing 1kg on the
Newton meter we see that 1kg weighs 9.8N.
(The difference between mass and weight is not discussed.)
NEWTON’S THIRD LAW OF MOTION
A car journey is used to illustrate the ideas of inertia and
momentum.
When a car is stationary the force of the car’s weight
pushing down is equal to the force of the ground pushing up. The result of the two forces is no movement
so the forces are in a state of equilibrium, or inertia. Once the car is
started and the driver accelerates or brakes you can feel the forces acting
upon you either pushing you back in your seat or throwing you forward. Now the forces are no longer balanced. The
car reaches a steady speed again and you can no longer feel any forces acting
upon you. All the forces are now in a
state of equilibrium known as momentum.
We sum up: to every action there is an equal and
opposite reaction.
FRICTION
Friction is the force which prevents movement between
surfaces. We are informed that this can
be either a good thing or a bad thing:
eg. Friction is needed to keep a car’s tyres on the road so that the
vehicle may grip to move forward but it causes problems between the moving
parts of a car’s engine where a lubricant has to be used to minimise the force
of friction.
TURNING FORCES
If a force is applied to an object at one point and the
object is fixed elsewhere the effect is a turning motion around the fixed
place, or fulcrum. The size of a turning force is called a moment.
Turning effects are used to our advantage in lever systems
and the law of moments is used in creating a set of scales.
There are three types of lever:
First
class lever: fulcrum rests between effort and load
Second
class lever: load rests between
fulcrum and effort
Third
class lever: the effort comes
between the load and the fulcrum
In the play a first class lever system is set up to lift a
weight. Using a pole for the lever and
a trestle as the fulcrum we demonstrate how the lever acts as a force magnifier
to move a heavy weight. The lever is 3
times longer on one side of the fulcrum than on the other and a simple
calculation is made to determine the magnification of the effort used when the
lever lifts the weight.
THE LAW OF MOMENTS
Moment =
force x distance from the fulcrum
A simple balance is made to demonstrate the law of
moments. Using a plank and the trestle
we construct a see-saw which balances when the moments on both sides are equal.
Two forces of equal magnitude are then placed on either end
and as the moments are still equal the see-saw remains balanced.
When the force is doubled on one side we see that the
see-saw no longer balances and, together with the audience, using the law of
moments we calculate the distance that the larger weight has to be from the
fulcrum to regain the state of equilibrium.
The force is moved half way in towards the fulcrum and we see that
indeed the moments are once again equal and the see-saw balances.
PRESSURE
A force acting over a particular area is called pressure.
The way that pressure increases or decreases according to
the size of the surface area it acts over is demonstrated:
A volunteer from the audience is asked to stand on a
polystyrene tile in a flat shoe. We see
that s/he has not marked the tile - their pressure was not great enough to
cause an indentation in the tile. So
the experiment is repeated using a high-heeled shoe. This time it is evident that the heel of the shoe has made a hole
in the tile and, as the pushing force (or weight of the person) is a constant,
it is the pressure that has become greater.
From this we conclude that the larger the surface area the
lower the pressure.
The French scientist Blaise Pascal gives his name to the units
of pressure:
pressure = force/area
(N/m2)
= (N) (m2)
One pascal (Pa) =
one Newton (N) per square metre (m2)
FLOATING AND SINKING
An object will float if it is less dense than water and sink
if it is more dense.
When an object is placed in water its weight pushes down on
the water and displaces some of it. The
water, however, pushes up on the object with a force that is equal to the
weight of the displaced water. This force is called the upthrust.
If an object is less dense than water the upthrust will keep
it floating on the surface. The weight
of the object equals the weight of the water is pushes away.
Anything that is denser than water will not be held up by
the upthrust because it weighs down with a greater force than the upthrust from
the water. These objects are heavier
than the water they displace when they are placed in the water.
However, by increasing the volume of water displaced the
upthrust of the water can be increased and an object can be made to float. Thus a ship made of iron, which is a
substance much denser than water, can be made to float because the density of
the iron hull and the air inside the ship and also the volume of water that the
ship now displaces combine to decrease the ship’s density and increase the
upthrust of the water enough to keep the ship afloat..
Density is
worked out as overall mass / total volume
Using a pastiche of the film Titanic, we discuss the nature
of density and how it relates to floating and sinking.
WORK
Work is said to have been done when a force effects a
movement or change in the direction that it is acting.
If a car moves along the road then work is done by the
engine in overcoming the friction created between the car’s wheels and the
road. The further the car travels the
more work is done:
work done =
force x distance moved in direction of force.
Work is measured in Joules , named after James Prescott
Joule, who found that no matter what work was done heat was produced and that
the sum of the work done and the heat produced equals the energy used to do the
work.
A historical vignette gives us Joule measuring the
temperature of a waterfall at the top and bottom to prove that the falling
water has produced heat energy making the waterfall warmer at the bottom than the top.
SPEED AND DISTANCE CALCULATION
We do not develop the relationship
between speed and distance but we do set up a simple calculation:
Using the relationship between distance covered by an
aircraft and the time available to cover the distance we calculate the average
speed required to complete the journey.
Show Requirements
The actors will be arriving approximately fifty minutes prior
to the start time in order to set up and will need to have access to the school
hall from then. They bring the set, lighting and sound equipment with them
so only need access to a plug socket. They’ll also need a space approximately
15’ wide by 10’ deep with the students sitting in front, usually in rows. The
show works well on a stage but if it’s more convenient for you to have them
‘on the flat’, that’s fine too.