what can a force can do to an what is the unit of force? · what can a force can do to an object?...
TRANSCRIPT
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:
The surfaces are jagged
when observed through
a microscope:
This leads to friction.
Friction song
PULLFRICTION
Friction Both No Friction
Ice SkatingMountain
Climbing
Olympic
Swimmer
Playing footballAirplane
Sticking poster
to the wall
Walking down
an icy street
Throwing
a frisbeeHorse riding
SledgingWriting
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)?
The mass of a convector
heater is 3900g.
Can you predict accurately
the weight of the heater in
newtons?
clamp stand
spring balance
100g masses
Astronomers have found: the
bigger the planet’s mass – the
larger is its gravitational field
strength – g !
EARTH - 10
JUPITER - 26
MARS - 4
VENUS - 9
SATURN - 12
URANUS - 12
NEPTUNE - 12
MERCURY - 4
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 On Jupiter: weight = 25x mass
Smaller planets small multiplier 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
Pressure = _______Force
AreaN/cm2cm2
N
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 smallbecause 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?
Now try the problem sheet!
Pressure = _______Force
Area
Area = 3 x 2 = 6 cm2
= ___30
6
= ____5 cm2
2cm
3cm
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)
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
Pressure = _______Force
Area