Falling From Trees
Students’ Sheet
Introduction
Isaac Newton
You’ve probably heard the story about Newton. It goes something along the lines: young Newton
was sitting under an apple tree. An apple fell, hit him on the head and he hit upon the idea of
gravity.
But how did Sir Isaac Newton tell the story? In 1726 he told
hit story to William Stukely, who included it in his biography
of Newton. Stukely wrote, "After dinner, the weather being
warm, we went into the garden & drank thea [tea] under
the shade of some apple tree; only he & myself. Amid other
discourse, he told me, he was just in the same situation, as
when formerly the notion of gravitation came into his mind.
Why sh[oul]d that apple always descend perpendicularly to
the ground, thought he to himself; occasion'd by the fall of
an apple, as he sat in contemplative mood.”
So it seems the story is true, except that there is no
mention of an apple landing on him. Newton was well
known to be irritable and grumpy, so he would probably
have said if it had happened.
Falling fruits
Many fruits fall from trees straight down to the ground.
Some are carried by the wind in various ways. Depending
on their shapes, they may drift, flutter, glide, spin or rotate.
To understand why fruits behave differently when they drop
from the tree, there are three ideas to keep in mind:

The force of gravity pulls objects towards the centre of
the Earth;

Anything dropping to the ground falls through air;

On a windy day the air is moving.
Flowers, cones and seeds
Many trees produce flowers.
When a flower is fertilised,
ovules in the pistil become
seeds and the flower becomes
a fruit in which the seeds
contained. Some trees such as
conifers produce cones and not
flowers. Fertilisation happens
when wind carries pollen from a
male cone to a female cone.
Ovules in the female cone
become seeds. Hard scales
protect the seeds.
Every seed has a protective
coat inside which is an embryo
and nutrients essential for its
growth. When released from its
fruit, a seed germinates
(embryo starts to grow) and
produces a seedling which
grows into a mature plant.
So to understand how things fall you need to know about gravity, air and the shape of objects
that are falling. And that includes fruits and leaves from trees.
Seed dispersal
Fruits and the seeds in them spread away (disperse) in various ways.
Rolling: Some fruits fall straight to the ground, but roll away.
Animals: Some fruits are eaten by animals and their seeds dispersed in the animals’
droppings. Others hook to an animal’s fur or fleece and are knocked or pulled off later.
Wind: Some fruits dry out. They fall off, but not straight to the ground. Instead they are
carried away by the wind.
Water: Some fruits float and are carried in streams and oceans.
Science & Plants for Schools: www.saps.org.uk
Falling From Trees: p. 1
Activities
Activity 1: Does mass matter?
Fruits such as apples, oranges, coconuts and acorns fall from
trees straight to the ground.
Nuts are fruits
Do heavy fruits fall faster than lighter ones? A group of students
decided to investigate.
Sounds odd? Perhaps, but
it’s true. Nuts are simply
fruits that have developed
a very hard shell.
To make it a fair test they agreed that fruits with the same size
and shape, but different masses should be used. But these are
not easy to find.
So instead they decided to model fruits falling using different
balls. They chose a table tennis ball, a squash ball and a golf
ball. All have the same diameter, but a different mass.
Carry out your own investigation using a table tennis ball, a
squash ball and a golf ball.
1. Measure and record the mass (in grams) and diameter (in
centimetres) of each ball.
Mass and weight
Weight is gravitational
force between an object
and the Earth. The more
mass an object has the
greater its weight. An
object with mass 1
kilogram has a weight of 10
newtons.
2. Drop them from the same height. Do the same from a greater
height and then again from an even greater height. In each case, record what happened.
Questions
1. Explain why using the three balls rather than three similar sized fruits made it a fairer test.
2. How does the mass of an object affect how long it takes to reach the ground?
3. Why do the balls fall to the ground when they are dropped?
Activity 2: Do size and shape matter?
The students concluded that mass did not affect how quickly objects fall. Do you agree with
them?
Next they wondered about size. They dropped a football and a tennis ball from the same height.
Again, both reached the ground at the same time. It seemed that size didn’t matter either.
Try it yourself.
But what about objects that have very different sizes and shapes? There was an oak tree in the
students’ neighbourhood and they collected some leaves and acorns. Just by holding them, the
students could tell that an acorn had more mass than an oak leaf.
They experimented and found that an oak leaf fell more slowly than an acorn. The acorn has a
greater mass than the leaf, but the students had already found that mass does not matter. One of
them noticed that while the acorn fell in a straight line to the ground the oak leaf fluttered down.
Try it yourself.
They began to wonder if their previous idea that mass doesn’t matter had been wrong. Was it the
greater mass of the acorn that made it fall more quickly than the oak leaf?
Then they hit upon an idea. They found two oak leaves of the same size and dropped them from
the same height. Both fluttered to the ground at the same time. Now they scrunched up one leaf
into a ball and repeated the experiment by dropping the two leaves – one un-scrunched and one
scrunched up – at the same time. The scrunched up leaf reached the ground first. One student
also noticed that the scrunched up leaf seemed to slow down and flutter as it began to ‘unscrunch’.
Science & Plants for Schools: www.saps.org.uk
Falling From Trees: p. 2
Try it yourself. You could use any pair of leaves provided that have near enough the same size
and shape. You could also try using two sheets of A4 paper. Crumple one sheet into a tight ball
and compare it with the un-crumpled sheet.
How can we explain this behaviour? Well, you need to think about air. After all, the ball, leaves
and pieces of paper do not fall through empty space. They fall through air.
Questions
1. Why might comparing a sheet of A4 paper with a crumpled up ball of A4 paper be a fairer test
than comparing an un-scrunched leaf with a scrunched up leaf?
2. One sheet of A4 paper was crumpled one up very tightly into a small ball. Another sheet was
also crumpled but less tightly to bigger ‘ball’. What would happen if both balls of paper were
dropped from the same height at the same time?
3. What have you learned about factors that affect how quickly things falling from trees?
Activity 3: Using the particle model to explain
You should be familiar with the particle model of solids, liquids and gases. It can be used to
explain how object fall through air.
Air is a gas. It’s a mixture of nitrogen and oxygen, with much smaller quantities of other
substances. The particles are nitrogen molecules, each made from two nitrogen atoms, and
oxygen molecules, each made from two oxygen atoms. We can represent these particles as N2
and O2.
Nitrogen molecule, N2
Oxygen molecule, O2
Atoms and molecules are not
coloured. However, we often
use colours to label spheres so
that we know which element’s
atom they represent.
Paper, oak leaves and acorns are solids. They are mixtures of many different compounds. The
particles of these compounds are made from atoms of carbon, hydrogen and oxygen. In some of
the compounds atoms of other elements are also used, but in very much smaller quantities.
Questions
1. Sketch two diagrams to show the arrangement the particles (a) in air, (b) in a solid.
2. Describe the how the movement of particles in a solid differs from particles in a gas.
3. Use the particle model of matter to describe what
happens when a solid object falls through air.
Hint: Look at the description of air resistance. What are ‘the
frictional forces’?
4. Explain why a crumpled sheet of paper falls faster than
sheet of paper and why an acorn falls faster than an oak
leaf.
Air resistance
Air resistance is caused by the
frictional forces of air against a
moving object. The faster the
object moves the greater the air
resistance.
Science & Plants for Schools: www.saps.org.uk
Falling From Trees: p. 3