Laws of Motion - Kindle Education

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Transcript Laws of Motion - Kindle Education 

Laws of Motion
Standard 9
Force
A push or pull that can cause an object to
change its velocity or which can cause a
flexible object to deform.
Balanced Forces
Force F1
Force F2
F1 and F2 are acting on the rope. If both teams are evenly matched then F1 = F2. But F1
and F2 are in the opposite direction and hence cancel each other.
The net force on the rope = 0.
When a number of forces act on a body such that the net force acting on the body is 0,
then such a combination of forces are known as balanced forces.
Types of Forces
Contact Forces
Muscular
Frictional
Non-Contact Forces
Magnetic
Gravitational
Electrostatic
Objects are Lazy – 1
Rough Ground
Smooth tiled floor
Football will remain at the same place unless someone kicks it.
The football stops rolling after sometime as friction opposes its motion.
The football travels more distance on a smooth surface as the frictional force is smaller.
If there was no friction, the football would keep on rolling.
First the football does not want to move and once moving it does not want to stop
(unless some force is applied).
Objects are Lazy – 2
Little guy
Toy vehicle
What will happen when the bus hits
the wall?
Wall
Stack of books
The bus stops moving when it hits the
wall. However the little guy on top of
the bus continues moving and
topples over.
Newton’s First Law of Motion
An object remains at rest or in motion in a straight line with a
constant speed until acted on by an unbalanced force.
Tendency of an object to resist change is called Inertia.
π‘°π’π’•π’†π’“π’Šπ’‚ ∝ 𝑴𝒂𝒔𝒔
Newton’s Second Law of Motion
More force is required to move or stop an object with
more mass.
𝑭𝒐𝒓𝒄𝒆 ∝ 𝑴𝒂𝒔𝒔
You need to kick harder if you want the football to
travel at a greater speed / velocity.
𝑭𝒐𝒓𝒄𝒆 ∝ π‘ͺπ’‰π’‚π’π’ˆπ’† π’Šπ’ π’—π’†π’π’π’„π’Šπ’•π’š
You will have to pedal harder if you want to reach the
top speed in less time.
𝟏
𝑭𝒐𝒓𝒄𝒆 ∝
π‘»π’Šπ’Žπ’† π’•π’‚π’Œπ’†π’
𝑭𝒐𝒓𝒄𝒆 ∝
𝑴𝒂𝒔𝒔 βˆ— π‘ͺπ’‰π’‚π’π’ˆπ’† π’Šπ’ π’—π’†π’π’π’„π’Šπ’•π’š
∝ 𝑴𝒂𝒔𝒔 βˆ— π‘¨π’„π’„π’†π’π’†π’“π’‚π’•π’Šπ’π’
π‘»π’Šπ’Žπ’† π’•π’‚π’Œπ’†π’
Newton’s Second Law of Motion
Momentum is defined as the total quantity of motion.
π‘€π‘œπ‘šπ‘’π‘›π‘‘π‘’π‘š = π‘€π‘Žπ‘ π‘  βˆ— π‘‰π‘’π‘™π‘œπ‘π‘–π‘‘π‘¦
πΆβ„Žπ‘Žπ‘›π‘”π‘’ 𝑖𝑛 π‘€π‘œπ‘šπ‘’π‘›π‘‘π‘’π‘š = π‘€π‘Žπ‘ π‘  βˆ— πΆβ„Žπ‘Žπ‘›π‘”π‘’ 𝑖𝑛 π‘£π‘’π‘™π‘œπ‘π‘–π‘‘π‘¦
The rate of change of momentum is directly proportional to the
impressed force and takes place in the direction in which the
force acts.
Newton’s Third Law of Motion
Straw
String
Force of air on balloon
pushes it forward
Wall
Atmospheric pressure
pushes the air out
As the air escapes from the balloon it pushes the balloon forward.
Newton’s Third Law of Motion
Ball pushes the
ground downwards
Ground pushes the
ball upwards
When moving down, gravity acts in
the direction of motion accelerating
the ball.
When moving up, gravity opposes the
motion decelerating the ball.
Newton’s Third Law of Motion
Block pushes the
water downwards
Water pushes the
block upwards
When you take off your hand the
force of the water pushes the block
upwards.
The harder you push the block
downwards, more the force with
which water pushes the block back.
For every action there is an equal and opposite reaction.
Action and Reaction act on different bodies and hence do not cancel each other.
Conservation of Momentum
𝐹2 = βˆ’ 𝐹1
π‘š2 π‘Ž2 = βˆ’ π‘š1 π‘Ž1
𝑣2 βˆ’ 𝑒2
𝑣1 βˆ’ 𝑒1
π‘š2
= βˆ’ π‘š1
𝑑
𝑑
π‘š2 𝑣2 βˆ’ 𝑒2 = π‘š1 𝑣1 βˆ’ 𝑒1
π‘š2 𝑣2 βˆ’ π‘š2 𝑒2 = π‘š1 𝑣1 βˆ’ π‘š1 𝑒1
π‘š1 𝑣1 + π‘š2 𝑣2 = π‘š1 𝑒1 + π‘š2 𝑒2
If there is no net force acting on two interacting bodies then their
total momentum is conserved.
Units of Measurement
Physical Quantity
SI Units
CGS Units
Force
kg m/s2 or Newton
g cm/s2 or dyne
Momentum
kg m/s
g cm/s