Weekly plan 3
Introduction to circular motion
Student book links
Specification links
Link to GCSE/AS specification
Suggested time allowed (includes contact and non-contact time):
•
•
•
Four hours
1.2.1–4
4.2.1 (a)–(f)
•
GCSE Forces and motion: forces,
speed, acceleration
AS 1.1.3 Kinematics
1.1.4 Linear motion
1.2.1 Force
Weekly learning outcomes
Students should be able to:
• Define the radian.
• Convert angles from degrees into radians and vice versa.
• Explain that a force perpendicular to the velocity of an object will make the object describe a
circular path.
• Explain what is meant by centripetal acceleration and centripetal force.
• Select and apply the equations for speed and centripetal acceleration: v = 2πr/T and a = v2/r.
• Select and apply the equation for centripetal force: F = ma = mv2/r.
Key words
Radian
Degree
Radius
Force
1.
2.
3.
4.
5.
The radian
Motion in a circle
Centripetal acceleration
Centripetal force
Examples of circular motion
How Science Works
Revolution
Circular path
Circular motion
Constant speed
•
Centripetal force
Centripetal acceleration
Velocity
Acceleration
Learning styles (S = Starter activities, M = Main activities, P = Plenary activities)
Kinaesthetic
Activity M2
Suggested teaching order
Interpersonal
Activity S3
Auditory
Activities S1–2
Activity M1
Activity P2
Visual
Activity M2
HSW 3, 5b Develop how to record, analyse and evaluate
primary data and recognise causal relationships (see Activity
M2 below).
ICT activities
•
Visit Multimedia Science School 16–18 and Absorb Physics to
purchase interactive software.
The web links referred to here are some that the author has found personally helpful but are not intended to be a comprehensive list, many other good
resources exist.
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Weekly plan 3
Suggested starter activities
Equipment
Teacher notes
1. Discuss acceleration as a rate of change of velocity.
Bung on string
Ask students under which circumstances is velocity
changing – get them to supply some examples. Give simple
examples of circular motion – the key idea should include:
changing direction so changing velocity therefore
accelerating, requiring a net force.
2. Brainstorm: ‘Why are there 360 ° in a circle?’ – leading to
the idea that 360 ° is arbitrary, so a scientific unit of angle is
required.
Include definitions of the radian and conversions – there are
many theories why there are 360 ° in a circle, including the
number of days and because it is divisible by 1, 2, 3, 4, 5, 6,
8, 9, 10, 12, 30, 60, etc. Research the history of the degree
on Wikipedia.
3. In pairs, get students to discuss the factors that affect the
size of the force required to make an object move in a circular
motion.
Can also predict the relationship between their variable and
the force required – leads on to Activity M2 below.
Suggested main activities
Equipment
Teacher notes
1. Get students to list as many examples of circular motion as
they can in two minutes – they have to identify the type of
force in each case that is perpendicular to velocity.
PC and projector
Many examples including: cars around bends; cars over
hills; planets; electron in orbit; bung on string, etc. Good
examples of situations where the required force can not be
provided include rally jumps and oil skids – search online for
clips of rally jumps and cars skidding.
Extend by asking students to consider what happened if the
force required cannot be provided – e.g. skids, jumps, etc.
2. Practical activity 4: Motion in a circle
See technician worksheet.
See teacher worksheet.
3. Questions on and use of F = ma = mv2/r equations –
including conical pendulums
Pendulum
Include calculations of v for objects moving in circles. Extend
by looking at the readings of scales used to measure the
mass of a 60 kg standing on the equator.
Suggested plenary activities
Equipment
Teacher notes
1. Quick conversion challenge
Table of 10 angles
Give students a table of 10 angles: five in radians and five in
degrees. They must then convert one to the other, with a
small prize given for the fastest correct answers. Include
common angles – i.e. 90, 180, 360 degrees, etc.
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Weekly plan 3
Start by asking the students to describe the forces on an
astronaut in the space shuttle – include lifts in free fall and
real weightlessness in deep space.
2. Discuss apparent weightlessness.
3. Get students to calculate the velocity of the planets around
the sun and the size of the force required to keep them in
orbit.
Data on the Earth and other planets –
look online for planetary data.
This is developed in more detail in Weekly plan 5.
Homework suggestions
•
•
Design a simple roller coaster with loops, including calculations for the acting forces. (Interactive: Build your own rollercoaster or Rollercoaster Physics (however,
these are quite simple and lack calculations)).
Practise using centripetal force equations.
Cross-curriculum links
•
Mathematics – circular motion calculations
Stretch and Challenge
•
•
Derivation of a = v2/r
Discuss motion in a vertical circle and the tension in the string at each point. Do some simple calculations to determine where the string is most likely to break.
Potential misconceptions
•
•
Weaker students will still assume the speed has to change for the object to be accelerating – reinforce the idea that acceleration is a change in velocity; this may
include a change in direction at constant speed.
When asked to draw free body diagrams of an object in circular motion, students often include an outward force to balance out the centripetal force – stress the need
for a net force or the object would not accelerate.
Notes
© Pearson
Education
Ltd 2009
© Pearson
Education
Ltd 2009
This document
may have
from the
original
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may been
have altered
been altered
from
the original
33