CIE IGCSE Physics
Turning Forces
Circular Motion and
Gravitational attraction
Centripetal Force
Recap of Forces
The meaning of centripetal force
The three factors on which centripetal force
depends
1
2
3
Why an object moving in a circle has an inward
acceleration
Task
Complete sheet on
Terminal Velocity
Centripetal Force
CENTRIPETAL FORCE is the general
name given to a centrally directed force
that causes circular motion.
Tension provides the
CENTRIPETAL FORCE
required by the
hammer thrower.
Other examples of centripetal force
Situation
Centripetal force
Earth orbiting the Sun
GRAVITY of the Sun
Car going around a bend.
FRICTION on the car’s tyres
Airplane banking (turning)
PUSH of air on the airplane’s
wings
Electron orbiting a nucleus
ELECTROSTATIC attraction
due to opposite charges
Factors affecting centripetal force
Centripetal force
INCREASES if:
- the object is moved FASTER
- the object’s mass is INCREASED.
- the radius of the circle is
DECREASED.
Centripetal Force
Why does an object moving in a circle have
an inward acceleration ?
When an object moves in a circle, there is
unbalanced force on it that acts towards
the center of the circle.
Newton 2 what happens if an object has an
unbalanced force on it?
Acceleration- How?
Acceleration is the change in velocity / time
Remember
velocity is a vector – speed and direction
So we have ……..
What happens if the string
breaks?
What direction does the ball move?
Remember Newton 1
String breaking quiz
Draw on the diagram provided
Tasks
Do questions 1- 4 on page 49
Question 12 on page 51
Fill in missing words
Choose appropriate words to fill in the gaps below:
circular
An object will only move along a __________
path if it is
force
constantly acted on by a centripetal _________.
The force is
towards
always directed __________
the centre of the circular path.
increases
Centripetal force ___________
if the object moves in a smaller
greater
radius path or at a __________
speed.
centripetal force is the Moon orbiting the
An example of a _________
gravitational
Earth due to the Earth’s _____________
pull on the Moon.
WORD SELECTION:
gravitational force
greater circular
towards centripetal increases
Centripetal Force
Recap of Forces
The meaning of centripetal force
The three factors on which centripetal force
depends
1
2
3
Why an object moving in a circle has an inward
acceleration
Circular Motion Simulations
Ladybug Revolution - PhET - Join the ladybug in an exploration of rotational
motion. Rotate the merry-go-round to change its angle, or choose a
constant angular velocity or angular acceleration. Explore how circular
motion relates to the bug's x,y position, velocity, and acceleration using
vectors or graphs.
Motion in 2D - PhET - Learn about velocity and acceleration vectors. Move
the ball with the mouse or let the simulation move the ball in four types of
motion (2 types of linear, simple harmonic, circle). See the velocity and
acceleration vectors change as the ball moves.
Motion produced by a force - linear & circular cases - netfirms
Uniform circular motion - Fendt
Carousel - centripetal force - Fendt
Relation between speed and centripetal force - NTNU
Vertical circle & force vectors - NTNU
Circular Motion & Centripetal Force - NTNU
Inertia of a lead brick & Circular motion of a water glass - 'Whys Guy' Video
Clip (3 mins) (2nd of 2 clips)
Gravitational attraction
• Gravity is an attractive force
• Gravity depends on mass and
the distance between objects.
Gravitational field strength
Gravitational field strength is equal to the force exerted on
an object of mass 1kg.
On the Earth’s surface the gravitational field strength is
about 10 N/kg (okay 9.81 N/kg)
Moon’s surface = 1.6 N/kg
Mars’ surface = 3.7 N/kg
Weight is the force of gravity on an object.
Gravitational attraction
Gravity is a force exerted by all objects on each
other.
Gravitational force:
- is always attractive
- increases if the mass of the objects is
increased
- decreases if the distance between the
objects is increased – it is inversely
proportional
- P.S These are Sir Isaac Newton’s rules on
Gravity
Complete
Answers
Surface
Field Strength
(N/kg)
Object mass
(kg)
Object weight
(N)
Earth
10
80
800
Moon
1.6
80
128
Mars
3.7
200
740
Jupiter
25
60
1500
Pluto
0.07
80
5.6
Choose appropriate words to fill in the gaps below:
objects on each other
Gravity is a force exerted by all ________
masses
because of their ________.
decreases
Gravitational force __________
if the distance between the
increases if their masses are
objects is increased but __________
increased.
weight
_________
is the force of gravity on an object. On the Earth’s
newtons
surface an object of mass 1kg has a weight of 10 __________.
The Moon’s gravity is about one sixth the strength of the
mass
Earth’s because its _________
is much lower.
WORD SELECTION:
increases
newtons
masses
objects
mass
decreases
weight
Gravity Simulations
Free-fall Lab - Explore Science
Galileo Time of Fall Demonstration - 'Whys Guy' Video Clip (3 mins) - Time
of fall independent of mass - Leads slug and feather with and without air
resistance. (1st of 2 clips)
Distance Proportional to Time of Fall Squared Demonstration - 'Whys Guy'
Video Clip (3:30 mins) - Falling distance proportional to the time of fall
squared. (2nd of 2 clips some microphone problems)
Lunar Lander - PhET - Can you avoid the boulder field and land safely, just
before your fuel runs out, as Neil Armstrong did in 1969? Our version of this
classic video game accurately simulates the real motion of the lunar lander
with the correct mass, thrust, fuel consumption rate, and lunar gravity. The
real lunar lander is very hard to control.
Moonlander Use your thrusters to overcome the effects of gravity and bring
the moonlander safely down to earth.
BBC KS3 Bitesize Revision:
Mass and gravity
Weight