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