Unit
9
FORCES
AND MACHINES
Short
Questions:
Q1. Define force?
A force is a push or
pull which changes the size, shape or speed of an object.
Q2. What is lever?
A lever is a bar that
turns on pivot called a fulcrum to exert the force.
Q3. What is machine?
A device which changes
a force applied to it to make work easier.
Q4. Write names of
simple machine?
There are six simple
machines.
1. Lever
2. Ramp
or inclined plane.
3. Wedge
4. Screw
5. Wheel
and axle
6. Pulley
Q5. What is screw?
A simple machine
consisting of a shaft with spiral groove is known as screw.
Q6. What is capstan?
A capstan is used to
raise heavy anchors of ships. A capstan is a revolving barrel with a vertical
axis.
Q7. What are conditions
for work to be done?
1. There
must be a force acting on an object.
2. The
object must move.
3. The
object must move in the direction of force.
Q8. What does scientist
mean by word “work”?
To a scientist, work is
the energy transfer which takes place when a force causes on an object to move
a certain distance in the direction of a force. Work can only be done if a
force act on something and move it.
Q9. How effort and load
are related with each other in lever?
The effort force (push
or pull) acts on one end of the lever and other end goes up or down in the
opposite direction like a see-saw.
Q10. In what way
machine make our work easier?
Machine make our work
easier by changing the direction of force. It can also make our work easier by
increasing the distance of the area where force is applied.
Long
Questions:
Q1. Write down note on
classes of lever?
Classes of lever:
Levers are divided into
three classes.
First class lever:
In first class lever,
the fulcrum is in between the effort and the load.
Characteristics:
1. It
produces a larger force from a small force.
2. The
effort moves further than the load.
3. The
fulcrum is nearer to the load to increase the turning effect of the effort.
Examples:
1. Scissors
2. Box
opener
Second Class lever:
In second class lever,
the load lies between the fulcrum and the effort.
Characteristics:
1. It
produces a large force from a smaller force.
2. The
fulcrum is usually closer to the load, which increases the turning effect of
the effort.
Examples:
1. Bottle
opener
2. Paper
cutter
Third class lever:
In third class lever,
the effort is in between the fulcrum and the load.
Characteristics:
1. It
produces a large movement from a smaller movement.
2. The
effort moves a shorter distance, but the load moves a greater distance.
3. A
large force is used to move a small load.
Examples:
1. Fishing
rod
2. Human
arm
Q2: Write down a note
on Archimedes screw?
One of the first screw
machines was invented by Archimedes.
Uses:
The Archimedes screw
was used to irrigate the fields, and to pump water out of a ship’s hold.
Construction:
This machine has a
watertight cylinder enclosing a spiral running from end to end, with its lower
end in the water. The machine was turned by hand, and the water collected in
the rotating spiral blades. These blades appeared to rise, as the screw turned.
The water poured out of a hole in the top of the cylinder.
Examples:
A jack screw, a piano
stool. etc.
Q3: Explain pulley with
the help of an example of fixed pulley?
A grooved wheel or set
of wheels around which a rope or chain passes in order to move a load.
Fixed pulley:
In a fixed pulley, the
pulley is attached to a hook or a wall and does not move. The clothes-line
pulley, flagpole pulley or the pulley on the mast of a sailing boat are like
this.
A fixed pulley simply
changes the direction of the force for instance you can pull down in order to
raise a flag a sail or a clothes line.
The advantage is that
it is easier to pull down on a rope to raise the load than it is to lift it up
in your arms.
A fixed pulley acts as
a first class lever and the fulcrum is the axle of the pulley.
