CIE IGCSE Physics

Turning Forces

Circular Motion and Gravitational attraction

Centripetal ForceRecap 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 ForceCENTRIPETAL 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:

An object will only move along a __________ path if it is constantly acted on by a centripetal _________. The force is always directed __________ the centre of the circular path.

Centripetal force ___________ if the object moves in a smaller radius path or at a __________ speed.

An example of a _________ force is the Moon orbiting the Earth due to the Earth’s _____________ pull on the Moon.

centripetal

circulargravitational

increasestowards

greater

WORD SELECTION:

force

centripetal

circular

gravitational

increases

towards

greater

force

Centripetal ForceRecap 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 SimulationsLadybug 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 strengthGravitational 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 attractionGravity 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

CompleteAnswersSurface Field Strength

(N/kg)Object mass

(kg)Object weight

(N)

Earth 10 80

Moon 1.6 80

Mars 3.7 740

Jupiter 60 1500

Pluto 0.07 80

800

128

200

25

5.6

Choose appropriate words to fill in the gaps below:

Gravity is a force exerted by all ________ on each other because of their ________.

Gravitational force __________ if the distance between the objects is increased but __________ if their masses are increased.

_________ is the force of gravity on an object. On the Earth’s surface an object of mass 1kg has a weight of 10 __________.

The Moon’s gravity is about one sixth the strength of the Earth’s because its _________ is much lower.

decreasesnewtons objectsincreases

mass weight

WORD SELECTION:

masses

decreases

newtons

objects

increases

mass

weight

masses

Gravity SimulationsFree-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