1.
What can a force can do to an
object?
2.
What is the unit of force?
3.
What are the different types of
force?
start
it moving,
stop it moving,
speed it up,
slow it down,
change its direction,
change its shape.
 The
newton (N) is the unit of force.
 Non-contact forces include –



gravity
electrostatic
magnetism
 Contact



forces include-
push and pull
friction between surfaces
friction moving through air .
1.
What are “balanced forces”?
2.
What happens when forces act on

a stationary object?

a moving object?
5,000N
3,000N
 When
all the forces acting on an object
“cancel each other out” they are said to be
“balanced”.
 When the forces on a stationary object are
balanced, the object will not move.
 When the forces on a moving object are
balanced the object will move at a constant
speed.
1.
What are “unbalanced forces”?
2.
What happens when forces act on

a stationary object?

a moving object?
 When
the forces on an object are unbalanced
the object will start moving and speed up.
 There is an unbalanced force on an object
when all of the forces acting on it do not
cancel out.
1.
What is “friction”?
2.
When is friction useful?
3.
When is friction not wanted and how can
it be reduced?
 Video:
Friction
 Friction is the force produced when two
surfaces rub on each other:
FRICTION
 The
surfaces are jagged
when observed through
a microscope:
 This leads to friction.
 Friction song
PULL
Mountain
Climbing
Ice Skating
Airplane
Playing football
Sticking poster
to the wall
Horse riding
Olympic
Swimmer
Throwing
a frisbee
Sledging
Writing
Friction
Walking down
an icy street
Both
No Friction
 Friction
is the force produced when two
surfaces rub on each other.
 Air resistance is a special kind of friction
caused when air passes around an object.
 Friction is often useful such as allowing shoes
to grip when walking.
 Friction can be a problem, for example when
it opposes motion.
 Streamlining
is the process of designing the
shape of an object so that air or water
passes smoothly over the object so friction is
reduced.
 Lubrication reduces friction by forcing rough
surfaces apart and allowing them to move
smoothly.
1.
What are “mass” and “weight”?
2.
How are mass and weight related?
3.
Are mass and weight the same
everywhere?
Video: Weighing air
 Mass
is the amount of matter measured in
Kilogrammes (Kg).
 Weight
is the force of gravity acting on the
object and is measured in newtons (N).
 But
how are mass and weight related?
 Let’s investigate!

REMINDER:
Mass is the amount of matter measured in
Kilogrammes (Kg).
 Weight is the force of gravity acting on the object and
is measured in newtons (N).


You’ve now found out: (note)

Weight on Earth (N) = mass (Kg) x 10

The 10 is called gravitational field strength or more
simply, g
But is g the same everywhere?
 Are your mass and weight the same everywhere?

 Can
we tell the weight of an
object (in N) if we already
know its mass (in g)?
spring
balance
clamp
stand
 The
mass of a convector
heater is 3900g.
 Can
you predict accurately
the weight of the heater in
newtons?
100g
masses
URANUS - 12
JUPITER - 26
EARTH - 10
VENUS - 9
NEPTUNE - 12
MARS - 4
MERCURY - 4
SATURN - 12
Astronomers have found: the
bigger the planet’s mass – the
larger is its gravitational field
strength – g !
 Weight
is the force of gravity on an object.
 Mass is a measure of the amount of matter in
an object and is measured in kilograms.
 On the Earth the weight of an object in
newtons is 10 times its mass in kilograms.
 The weight of an object on the Earth can be
calculated from weight = mass x 10.
The force of gravity, or weight of an object is
different on other bodies in the Solar System.
 Mass is the same everywhere.
 When calculating the weight of an object on
other planets or moons, rather than using x10,
other multipliers are used depending on the size
of the planet or moon.
 Bigger planets  big multiplier



Smaller planets  small multiplier


On Jupiter: weight = 25x mass
E.g. on Mercury: weight = 4x mass
Now find what you would weigh on different
planets and moons - research exercise,
w/c: Gravity and the Planets
1.
What effect does gravity have on falling
objects?
2.
How does friction affect falling objects?
3.
What affects the speed of a falling
parachute?
Video: Falling on the Moon
 What
design features of parachute affect its
average speed as it falls?
 Let’s
investigate!
 Task:
To make a simple parachute and to
investigate how its average speed of descent
depends on a chosen variable.
 Complete
the worksheet as you conduct
the experiment.
 The
force of gravity causes falling objects to
speed up.
 When an object falls, air resistance acts
against the force of gravity. This means the
object will not speed up as much.
 A parachute has a large area to make the air
friction very large so that it will balance with
the force of gravity to allow the parachute to
fall at a low constant speed..
1.
What is “pressure” and how is it
calculated?
2.
What is the unit of pressure?
3.
How do changing force or area affect
the pressure?
An elephant will exert less
pressure than a person
wearing high heels. This is
because the weight of the
elephant is spread over a
larger surface area.
Poem:
Sir jumps quickly to his feet
He’s got the point (-he’s got a scar!)
The pressure acting on his seat,
Is force per unit areaaaaaaaaagh!
 Pressure
is how much force is put on a
certain area, so
N
N/cm2
Force
Pressure = _______
Area
cm2
This man can lie comfortably on the bed of nails since his weight is
spread over many many nails.
video: Pressure 2
 For
a given force, a big area means a
small pressure:
 In
all of these cases the pressure is small
because the area is big.
 The force is spread out over a bigger
area so the pressure is low.
 For
a given force, a small area means a big
pressure:
 In
all of these cases the pressure is large
because the area is small.
 The force is concentrated over a small area so
the pressure is high.
 What
is the pressure of
the box on the bench?
Area = 3 x 2 = 6 cm2
2cm
3cm
Force
Pressure = _______
Area
30
= ___
6
cm2
= 5____
 Now
try the problem
sheet!
30N
Weight of box
Pressure is how much force is put on a certain
area.
 The unit of pressure is the newton per square
centimetre (N/cm2)

Force
Pressure = _______
Area

For a given force,
 a small area means a big pressure
 a big area means a small pressure

Some practical applications of high and low
pressure includes snow shoes, skis, stiletto
heels, studs on football boots, spikes on running
shoes, a bed of nails, camel’s feet