2.3 Mass and Inertia
-
Upload
emil-helmi -
Category
Documents
-
view
227 -
download
0
Transcript of 2.3 Mass and Inertia
-
7/28/2019 2.3 Mass and Inertia
1/16
Massand
Inertia
-
7/28/2019 2.3 Mass and Inertia
2/16
Mass
Mass is defined as amount of
matter in a body.
SI unit = kilogram (kg)
It is a scalar quantity.
-
7/28/2019 2.3 Mass and Inertia
3/16
Inertia
Inertia is the tendency of an object to
remain in its state of rest or of uniform
motion in a straight line.
Law of inertia is also known as Newton's
First Law of Motion
-
7/28/2019 2.3 Mass and Inertia
4/16
Newton's First Law of motion
state that
In the absence of external forces, anobject at rest will remains at rest and an
object in motioncontinues in motion with a
constant velocity (that is, with a constantspeed in a straight line).
-
7/28/2019 2.3 Mass and Inertia
5/16
Object at rest will remains at rest. Inertia of
an object will resist any tendency to
change it state of rest.
For an object in motion, inertia of that
object will remains the object in its state of
motion with uniform velocity.
-
7/28/2019 2.3 Mass and Inertia
6/16
Situations involving INERTIA
1) Jerking a cardWhen the cardboard is jerkedquickly, the coin will fall into the
glass.
Explanation:The inertia of the coin resists the
change of its initial state, which is
stationary.
As a result, the coin does not
move with the cardboard and falls
into the glass because of gravity.
-
7/28/2019 2.3 Mass and Inertia
7/16
2) Pulling a book
When the book is pulled
out, the books on top will
fall downwards.
Explanation:
Inertia tries to oppose the
change to the stationary
situation, that is, when thebook is pulled out, the
books on top do not follow.
-
7/28/2019 2.3 Mass and Inertia
8/16
3) Pulling a Thread 1. Pull slowly - Thread A willbreak.
Explanation:
Tension of thread A is higher
than string B.
Tension at A = Weight of the
load + Pulling Force
2.Yank quickly - Thread B will
break/ snap.
Explanation:
The inertia of the load prevents
the force from being transmitted
to thread A, hence causing
thread B to break/snap.
-
7/28/2019 2.3 Mass and Inertia
9/16
Larger Mass -> Greater Inertia
Bucket filled with sand is
more difficult to be moved.It's also more difficult to be
stopped from swinging.
Explanation:Object with more mass
offers a greater resistance to
change from its state of
motion.Object with larger mass has
larger inertia to resist the
attempt to change the state
of motion.
-
7/28/2019 2.3 Mass and Inertia
10/16
Another example is a high speed lorry will
takes longer time to stop compared to a
car with same speed because the inertiaof the lorry is much larger than the car.
Larger Mass => The Larger inertia
Smaller mass => the smaller the inertia
-
7/28/2019 2.3 Mass and Inertia
11/16
Relationship between Mass &
Inertia
A shopper in a supermarket observes that it is
always easier to start moving an empty trolley
than a full trolley.
Similarly, it is easier to stop an empty trolley
than the full one if both are moving at the
same speed.
Thus, the resistance to change its velocity i.e.
the inertia, is related to the mass of the
object.
-
7/28/2019 2.3 Mass and Inertia
12/16
Effects of inertia
THE POSITIVE EFFECT OF INERTIA
1. The head of hammer can be fitted
tightly onto the wooden handle by
hitting the bottom of the handleagainst a hard surface. The head
of hammer has big mass and will
remain in its state of motion, thus
fitting it tighter on the handle.
-
7/28/2019 2.3 Mass and Inertia
13/16
POUR OUT CHILLI SAUCE
2. - Chilli sauce in the bottle can be easily
poured out if the bottle is moved down fastwith a sudden stop.
- The sauce inside the bottle moves
together with the bottle.- When the bottle stops suddenly, the
sauce continue in its state of motion due to
the effect of its inertia.
-
7/28/2019 2.3 Mass and Inertia
14/16
Ways of reducing the negative
effect of inertia
Situation :
If a car crashes, inertia of the passengers causes
them to continue it motion. This is a
dangerous situation. Upon impact, the
passengers will crash into part of the car
immediately in front of them and suffer
injuries.
-
7/28/2019 2.3 Mass and Inertia
15/16
solution
A) Safety belt
Safety belt secure the driver and passengers
to their seats. When the car stops suddenly,
the seat belt provides the external force that
prevents the driver or passengers from being
thrown forward.
-
7/28/2019 2.3 Mass and Inertia
16/16
B) Air bag system
Air bags mounted on the dashboard or steering
wheel expand automatically when a collision
occurs. This prevents the driver or passengers
from crashing into the dashboard.