Force And Newtons Laws Of Motions IJSO Flashcards
Force definition
Force is an external effort in the form of push or pull that changes or tries to change the shape or size or the state of motion of an object.
Momentum definition
It is the quantity of motion possessed by a object. The quantity of motion depends on 2 variables mass and velocity.
More the momentum more hard would it be to stop the object.
2 types of velocity
Linear velocity
Angular velocity
Force us just the
Rate of change of linear momentum
Work =
Force x displacement
Force dimensional formula
[M¹L¹T⁻²]
Momentum dimensional formula
[M¹L¹T⁻¹]
Work dimensional formula
[M¹L²T⁻²]
Power dimensional formula
[M¹L²T⁻³]
Acceleration dimensional formula
[L¹T⁻²]
Force =
Rate of change of linear momentum =
∆p/time
Energy
Capacity of a body to do work.
Work-energy theorem
Work done = change in kinetic energy
1/2mv² - 1/2mu² = 1/2m(v²−u²) =1/2m (2as) =mas =F x displacement
Gravitational force definition
Force of interaction that exists between 2 particles due to their mass.
Electromagnetic field definition
A physical field formed by electrically charged objects
Electric charge
Physical property of matter that causes it to experience a force when placed in an electromagnetic field.
4 fundamental forces
Gravitational force
Electromagnetic force
Strong nuclear force
Weak force
Equilibrium :
The state at which the net force on an object is 0 is called equilibrium.
Newton’s first law of motion is also called as the
Law of inertia.
Inertia definition
Tendency of a body to oppose the change in its state or rest or uniform motion in a straight line.
“Natural length” of a spring
The length of the spring when neither pulled nor pushed.
Impulsive force definition
A large force acting for a short period of time to produce a finite change in the momentum of a body is called impulsive force.
Impulse definition
Change in momentum.
Impulse formula
Impulsive force x time
Impulse = change in momentum.
This relationship is called
The impulse equation or the momentum impulse theorem.
Impulsive force x time =
Impulse of force = change in momentum
1st law of motion
Every body remains in its state of rest or uniform motion in a unless compelled by an external unbalanced force.
If unbalanced forces do not act on a body then
The body will remain unaccelerated.
Inertia definition
Tendency of the object to oppose a change in its state of rest or uniform motion in a straightforward.
All forces only act in pairs called
Action reaction pairs or interaction pairs.
Newton’s 3rd law states that all actions acts in
Pairs.
Momentum-impulse theorem
Impulse = change in momentum
Newton’s 3rd law says ………… can never exist
A single force
Friction
A surface resistance that opposes the motion of an object due to its interaction with the surroundings.
Strings are usually regarded to be
Massless and unstretchable.
Tension
Magnitude of pulling force exerted by a string,cable,chain,rope etc.
If the length of a spring becomes less than its natural length, then it is called as the
Compressed spring , which pushes the objects at its end.
A moving car collides with a truck at rest which would have more damage.
According to the 3rd each of them exert equal force in the opposite direction.
But the force exerted on the car by the truck would cause more acceleration as the mass of the car is less. This sudden acceleration makes it more dangerous.
2 types of kinetic friction
Sliding friction
Rolling friction.
A system should contain a minimum of ….. objects.
2
System definition
Two or more objects that interact with each other form a system.
2 types of forces acting on a system
Internal forces :
Forces acting within a system among its constituents.
External forces :
Forces exerted on the constituents of a system by the outside environment.
Free body diagram (definition)
It is a diagrammatic representation of a single body or a subsystem of bodies isolated from surroundings , showing all the forces acting on it.
F(AB) means
Force exerted on A by B.
An object is said to be in equilibrium when the vector sum of all forces acting on it become
0
An object is said to be in rotational equilibrium when :
The vector sum of all torques acting on it become 0
When we walk does frictional force act forward or backward
You are standing (velocity=0); You suddenly start walking (velocity=v). You just accelerated from velocity 0 to v in the FORWARD direction. So there must have been an EXTERNAL (to your body) FORCE in the FORWARD direction which caused this acceleration.
What is this external force APPLIED ON YOU IN THE FORWARD DIRECTION that caused this acceleration and who applied it?
Answer- The external force is the Friction between your foot and the ground. And obviously the ground applied it on you. (You tried pushing the ground backward by making use of those irregularities on the surfaces of your foot and the ground, and the ground in turn pushed you forward(action reaction))
Now that you have started walking, you walk with the same velocity on an average, DON’T YOU ? (think)
So now you are not accelerating once you have started walking. The NET EXTERNAL FORCE must be zero then. Hence, ONCE YOU HAVE STARTED WALKING, YOU DON’T ACCELERATE; THEREFORE THE NET FRICTION ON YOU IS ZERO ON AN AVERAGE.
Your back foot is pushing you forward, so the frictional force on the ground is forward.
Your front foot is (INITIALLY) stopping you from falling, so the frictional force on the ground is backward.
When we act at a constant speed , the net frictional force is ….. , but while gaining speed net frictional force is …….
0, positive
It is because the frictional force pushes the rear leg forward (f1) and the frictional forces acts backward on the front leg (INITIALLY) to stop u from falling.(f2)
When you are walking with a constant speed they are equal (f1 and f2). So the net frictional force acting on the object is 0.
But while gaining speed f2 is lesser than f1 causing u to gain speed. Here the net frictional force is positive.
But while losing speed f2 is more than f1 causing u to loss speed. Here the net frictional force is negative.
Less force has to be applied to pull a object rather than push it why ?
When u push a object (not horizontally) a component of that force would increase the normal force of the body. This increase in the normal force causes the frictional force to increase. This increase in frictional force makes it harder to push an object.
While when u pull an object a component of the force would reduce the normal force , thus reducing friction. (As friction is less it is more easier to pull).
Less force is needed to pull an object rather than pushing it.
T
Spring balance measures the :
Weight of an object by measuring the force applied on the hook.
A weighing machine , measures the weight of an object by measuring the
Force applied on the upper surface of the machine.
(mg - T) or (T - mg) =
ma.
When an object is in translational equilibrium
Net forces acting on it are 0. That is ∑F(x) = 0 ∑F(y) = 0 ∑F(z) = 0
Translational equilibrium is divided into 2
Static equilibrium
Dynamic equilibrium
(Division based on the state of rest or uniform motion when at equilibrium)
Simper meaning
Insincere expression or behaviour.
Frictional force happens due to the
Molecular interaction between the surfaces at the area of contact.
At the actual points of contact between the 2 surfaces …….. are formed
Molecular bonds.
During friction the ………. is lesser than the total surface area
Actual area of contact
Molecular bonds formed at the actual contact points of the surface cause
Friction, when the body moves, these bonds get broken, and the material gets deformed and new bonds are formed.
The deformation of the material in frictional force sends ……. into the bodies.
Vibrations, and these vibrations dumps out and finally appears as heat.
Tension in a string is an
Electromagnetic force
Component of contact force m
Perpendicular to the surface:
Parallel to the surface:
Normal force
Friction
Normal force measures
How strongly the surfaces in contact press against each other.
All contact forces are
Electromagnetic forces.
As there is no such force called contact force in the fundamental forces of the universe.
Normal force in an inclined plane where the angle of slope θ:
mg cosθ
Non contact forces are also called
Field forces.
Contact forces definition
Forces which are transmitted between bodies by short range atomic interactions are called contact forces.
Field forces (non contact forces) definition
Forces which act on objects at a distance , due to the interaction of those objects with a, field produced by other objects.
Their are 6 contact forces :
Normal Frictional Spring Tension Buoyancy Applied force.
A pulled spring is called
Stretched or extended spring.
Spring force is …… in nature
Electromagnetic
Hookes law
F = -kx
k - spring constant
x - displacement
Limiting friction definition
When the applied force reaches a certain limit the object would be on the verge of motion. The frictional force at this stage is called limiting friction. When the body is set into into motion smaller force is now required to continue the motion.
Kinetic or dynamic friction
Force of friction experienced by a body when it is in the state of motion.
Conservative force definition
A conservative force is a force which does the same magnitude of work in moving an object between 2 points, regardless of the path taken.
E.g. gravity.
Work done = force x displacement
= mgh.
A conservative force when it completes a round , the total work done is
0
Change in potential energy = 0
Change in kinetic energy = 0
Non conservative force definition
A conservative force is a force in which the magnitude of work done in moving an object between 2 points, is based on the path taken.
E.g. friction.
Work done = (-) frictional force x distance covered.
How do u define interaction between bodies
When one body influences another body by applying force with or without contact, we say that that the 1st body is interacting with the second body.
Action and reaction forces act on
2 different bodies.
It is impossible to have a …… force
Single isolated force.
1 kgf :
Force by which 1kg is attracted to the centre of Earth.
F = 1kgwt = 10N
1gf
Force by which 1g is attracted to the centre of Earth.
F = 1kgwt = .1N
1 Newton = ….. dynes
10 raised to 5.
Nuclear force acts in
The nucleus ,that too for a very short order of 10 raised -15m.
It does not depend on charge and acts equally between protons,neutrons.
Electrons do not experience this force due to the short distance of nuclear force.
Strongest fundamental force
Nuclear force.
Gravitational and electromagnetic forces are
Long range forces.
All forces that we experience as a push or pull or by contact (except gravitational force) are manifestations of
Electromagnetic force
Neutrons and protons are a type of particles called
Hadrons
Colours are given to the quarks to describe the
3 different quantum states that quarks can exist in.
Why are quarks constantly changing color(quantum state) ?
The process by which they do this is by exchanging some particles called gluons. This holds then together.
Force carrier of strong force
Gluons
Gluon properties
No mass
No electric charge
But has color (quantum state)
Weak force changes the
Quark flavours
What are the different quark flavours
There are 6 flavours Up Down Charm Strange Top Bottom
There are 2 force carriers for weak force
W boson (positive or negative) Z boson (no charge)
Range of weak force
.1% of diameter of proton.
Weak forces changes the
Quark flavours.
Weak forces are actually able to change the identity of particles when they come very close to each other.
Ratio of
Strong nuclear force : electromagnetic force : weak force : gravitational force
1 : 10⁻² : 10⁻⁷ : 10⁻³⁸
Electromagnetic field depends on the
Nature of medium between the charges.
What is centre of gravity ?
A body is made of a number of particles and these particles are attracted towards the earth due to gravity. The forces acting on them are F1,F2,F3 etc. These forces act parallel in the downward direction. The parallel forces can be replaced by a single resultant force acting at a particular point of the body. This point is called centre of gravity.
A body is said to be in stable equilibrium if
The body returns to its original state after the external force causing change in position of the body is withdrawn.
A body is said to be in unstable equilibrium if
The body does not return to its original state after the ,external force causing change in position of the body, is withdrawn.
Neutral equilibrium.
A body is said to be in neutral equilibrium if the body takes a new position without changes in its centre of gravity.
What is happening in stable,unstable and neutral equilibrium
After applying a external force that causes a slight displacement in from the equilibrium position of an object:
1) If BOTH POSITION and CENTRE OF GRAVITY of the object does not tend to change (tends to return to original state) : stable equilibrium
2) If BOTH POSITION and CENTRE OF GRAVITY of the object changes (comes to a completely new state) : stable equilibrium.
3) If POSITION changes but CENTRE OF GRAVITY of the object does not change : neutral equilibrium.
Spring balance actually measures the force exerted by the object on its
Hook
Cartridge contains
Bullet, the casing , a chemical powder.
(Only the main things said here)
The chemical powder causes a chemical reaction propelling the bullet forward.
Recoil
A backward movement usually caused by momentum etc.
Why aren’t the normal force and gravity, action reaction pairs.
They are not action reaction pairs as normal force would not necessarily be equal to gravity.(in a lift)
Actually it is the normal force acted by the book on a table ,and, the normal force acted by the table on the book ,which are action reaction pairs.
Actually it is the force by which the earth attracts the book(mg) ,and, force by which the book attracts the earth(mg) ,which are action reaction pairs.
In a free body diagram only …….. forces are represented
External
Recoil velocity of a gun when it fires a bullet is taken
Positive. (I know that the bullets and the recoil of the gun move in the opposite directions but both of their velocities are put as positive)
:(
F = kma. Here k is the
Proportionality constant
A bullet fired from the gun makes a small hole, while a stone shatters the wall
it because of impulse
impulse = force * dt
for bullet the time factor is too small thats why impulse is small than that of stone.. or in normal language when bullet touches the glass the duration(dt) of application of force is too small …
again suppose i fire a large bullet… here area of impact is large
force= pressure * area - > that implies
impulse = pressure * area * dt
so there r two variables area and dt … pressure is constant because glass can bear a constant amount of pressure before it breaks … does not matter u fire a bullet or through a stone.
A stone has more area and takes more time , so the impulse of the stone is more and this causes the glass to shatter.
Also as the bullet is moving very fast it is not able to impart its motion and the glass remains at rest due to inertia of rest.
Force = mass x acceleration =
Pressure x area
In an accelerating system acceleration can be found by
F/(m1 + m2)
Taut meaning
stretched or pulled tight.
Total interior angle of a polygon
(n-2) x 180
Under the action of weak force, a neutron changes into
A proton emitting an electron and a particle called antineutrino.
Value of coefficient of friction, theoretically extends from
0 to infinity.
But it’s practical value stretches from :
0 < μ ≤ 1.6.
The force carriers of gravitational force
Although not yet found, the “graviton” should be the corresponding force-carrying particle of gravity
The force carriers of gravitational force
Although not yet found, the “graviton” should be the force-carrying particle of gravity
F =
(change in kinetic energy)/displacement
Velocity = (in terms of momentum)
Momentum/mass
Sophomoric meaning
Juvenile
Inertia frame is that which is at
Rest or uniform motion (no acceleration)
Non inertial frame is that which is at
Accelerated motion.
Normal forces
If the contact forces between the bodies are perpendicular to the surfaces in contact ; then they are called normal forces.
Unbalanced forces definition (MTG)
When 2 forces of equal magnitude act on an object in the opposite direction, then the object continues to be in the state of rest or uniform motion in a straight line. Such forces are called balanced.
Unbalanced forces definition (MTG)
When 2 forces of unequal magnitude act on an object in the opposite direction, then the object moves in the direction of the larger force.Such forces are called balanced.
Study of cause of motion
Dynamics
Inertia definition (net)
Property of mass that resists acceleration
Law of conservation of momentum
The total momentum of a system remains constant if no external force acts on it.
SI unit of inertia
kg (I don’t actually understand)[MTG]
Inertia of a body is equal to the …… of the body
Mass (I don’t actually understand)[MTG]
Why doesn’t action and reaction cancel each other out
They don’t cancel as they act on 2 different bodies. Each force produces its own effect.
