The floating ball and gravity - University of Ulster

The oating ball and
GRAVITY
BEATING GRAVITY WITH A PING PONG BALL
Gravity is a force. It is the force that stops ever ything on earth from drifting off
into space and the force that pulls objects towards Earth. Your weight is the force
of gravity that acts on you. Your weight changes with your location in the universe.
OBJECTIVES
To understand the effect of forces,
including gravity, on a ball.
To enable children to assess their own
knowledge, skills and understanding.
STARTER
Play “get in order”. Invite the whole
group to stand up. Explain to the class that
we are going to get into order according to
date of birth. Label one side of the room as
1st January and the other side as 31st
December. Tell the children that there is one
catch: they must do this silently. Allow 2
minutes for this.
Alternative criteria for ordering: height,
hand size, distance from floor to belly button.
Using the whole room: assign one wall
to be the x axis and the wall perpendicular to
be the y axis. Label the corner as 0. Ask
children to plot how much fun they want to
have against how much they want to learn
with their body as the data point
STIMULUS
Why
doesn’t the ball
fall?
Demonstrate to the whole class how to
hold a ping pong ball in the air with no hands.
Plug in and turn on a hair dryer in, holding it
so that the nozzle is pointing upwards. Place
the ping pong ball (smaller than the nozzle)
into the airflow, holding the hair dryer steady
so that when you let go, the ping pong ball
hovers in the air. Slowly change the angle of
the hair dryer and see how far it can be tilted
before the ball falls.
Extension A: Challenge one pupil at a
time to see how long they can hover the ping
pong ball, pass the hair dryer with ping pong
to a friend, or how far they can tilt the hair
dryer before the ball falls off.
Extension B: Give each child a malteser
and a straw and challenge them to recreate
the effect.
What
is the
maximum
angle?
GENERATING QUESTIONS
Allow the children time to think of a
question individually. Give each pupil a post-
it note (use 5 different colours, with an equal
number of each colour) and ask them to
record their question on the post-it. Ask the
children to find others with the same colour of
post-it. Give the children 5 minutes in these
groups to agree on one question and ask
them to record it on A4 paper.
SELECTING QUESTION FOR DISCUSSION
What
forces are
involved?
Collect all the A4 question sheets, read
them aloud to the class and then display them
in the centre of the circle. Give each pupil 3
counters and explain that these counters can
be used to vote however they please, for
example all placed on one question or shared
over 2 or 3. The question with the most votes
will be the focus of the enquiry.
ENQUIRY
Manage turn taking by asking children to
pass a cuddly toy if they want to speak.
REFLECTING ON THE ENQUIRY
KSU: ask the children to reflect on the
knowledge they have gained, the skills they
have used to gain it and what they now
understand better. Write these thoughts on
an exit ticket (page 2) to be handed in to exit
the lesson (to go to break or lunch, or just to
mark the end of the enquiry lesson).
Resource for Teachers 1 www.ulster.ac.uk/scienceinsociety/

Exit Ticket
Knowledge I have
gained
Something I still want to know...
Exit Ticket
Knowledge I have
gained
Something I still want to know...
Skills I have used What I understand better
Skills I have used What I understand better
Resource for Teachers 2 www.ulster.ac.uk/scienceinsociety/

forces
and
motion
the
ping
pong
ball
Ball
Weight
• When the hair dryer is switched off, the
ball drops to the floor. This is because
the force of gravity pulls the ball towards
the Earth.
• When the hair dryer is switched on, the
ball hovers in an invisible cylinder.
• Gravity (the force due to the weight of
the ball) is the force that prevents the
ping pong ball from flying straight up
into the air (gravity pulls all objects
towards earth). This is balanced by
an upwards force from the hot air
coming from the hair dryer.
• When the angle of the hair dryer is changed slightly,
the ball remains in the invisible cylinder.
Upward force due
to air from hair
dryer
Ball
Weight
yellow arrows show the force from the
higher pressure air acting inwards on the
moving air and ping pong ball.
Upward force due
to air from hair
dryer
Weight
• This is because
moving air is at a
lower pressure than
still air. The air moving
around the ball, from
the hair dryer, is at a
lower pressure than
the surrounding air.
• The surrounding air
therefore pushes on
the moving air, holding
the ball in the cylinder.
This effect is called the
Bernoulli effect.
FORCES
The Bernouilli effect can be
seen with maltesers too.
Resource for Teachers 3 www.ulster.ac.uk/scienceinsociety/
Ball
1
a
malteser may be
“the light fantastic”
but it still has
weight
W
U
W
Blowing through a straw
takes the place of the hair
dryer. The fast moving air
stream is at lower pressure
than the surrounding air.