# what can a force can do to an what is the unit of force? .what can a force can do to an object? 2     Post on 22-Jul-2018

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• 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:

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

file:\\SEC-DC-001.CL15.INTERNAL\Media\PHYSICS\Weighing Air.mpg

• 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?

Lets 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).

Youve 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 planets 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

file:\\SEC-DC-001.CL15.INTERNAL\Media\PHYSICS\Falling on the Moon.mpg

• What design features of parachute affect its average speed as it falls?

Lets investigate!

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

larger surface area.

Poem:

Sir jumps quickly to his feet

Hes got the point (-hes 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/cm2 cm2

N

This man can lie comfortably on the bed of nails since his weight is

video: Pressure 2

file:\\SEC-DC-001.CL15.INTERNAL\Media\SCIENCE\Pressure 2.mpg

• 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, camels feet

Pressure = _______Force

Area

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