FORCES AND
ENERGY
UNIT-3
Created by : Ms. Ilma Ihsan
3. 1 Forces and motion
3.2 Speed
3.3 Describing movement
CONTENT S
3.4 Turning forces
3.5 Pressure between solids
3.6 Pressure in liquids and gasses
3.7 Particles on the move
3.1 FORCES AND
M OTION
QUESTIONS
1. What is a force ?
2. What is the unit of force ?
3 . How are forces shown on Diagrams ?
4 . One or more forces always act on any
object on Earth. Is this true ?
Fig 1: Forces acting on
Objects that are stationary
(Not moving)
Fig 2: Forces acting on Objects that
are moving
BALANCED OR
UNBALANCED ??
The force of gravity
pulling the object
towards the Centre of
the Earth is called its
WEIGHT.
• The object doesn’t
move towards the
Centre of the
Earth because the
ground is pushing up on
the object. This force is
called as the contact
force.
•
•
When the forces act in equal
sizes in opposite directions,
such forces are called
Balanced.
•
Objects can have more than
2 forces.
Eg : When a wind is blowing
across a rock and if the rock
doesn’t move Sideways, it
means that the Pushing force
from the wind is balanced by
friction between the rock and
the ground.
•
These forces can be
shown in Force
diagrams.
•
In a force diagram arrow
shows the size and
direction of each force.
•
The longer the arroow,
the bigger the force is.
S TARTING TO
MOVE
Eg: Imagine the rock is
now pushed with a
much larger force than
the wind, such as a large
vehicle.
• When the vehicle
pushes on the rock, the
pushing force will be
larger than friction.
•
The rock will now move because
the sideways forces are not
balanced.
The rock will now start to move
in the direction of the larger
sideways force.
The rock will not move up or
down because the forces acting
up and down are still balanced.
SLOWING
DOWN
•
Unbalanced forces can
also make moving
objects slow down.
CHANGING
DIRECTIONS
•
Unbalanced forces can also make objects change
direction
•
This tennis ball will change direction because of an
unbalanced force.
FORCE OF
GRAVIT Y
•
The force of gravity on a
planet is a constant,
unbalaced force.
•
When an object moves
in a cricle, its direction
always keep changing. A
constant unbalanced
force is needed to keep
an object moving in a
circle.
SUMMARY
• When forces are equal in size and opposite in direction, the forcesare balanced.
• Balanced forces causes no change in movement
When forces are not equal in isze and/or act in directions that are not opposite, the
forces are unbalanced.
Unbalanced forces cause change in movement ; speeding up
Slowing down
Changing directions