Dynamics Flashcards
Definition of Newton’s 1st law
Newton’s first law states that an object remains at rest or continues to move with a constant velocity unless an external resultant force acts on it.
Key points:
1)No resultant force is required to allow an object to continue its original motion.
2)Only forces that are exerted by other objects can change the state of motion of the object.
A coin is resting on a card on top of a cup. How can the coin be inside the cup without touching the coin and the cup?
The card has to be flicked during which the coin continues to stay its state of rest momentarily. Without the card’s support, the coin drops into the glass, due to its own weight.
How does friction affect the resultant force opposing the motion of the object?
With less friction, there is a smaller horizontal resultant force opposing the motion of the object. Hence, the object stops at a further distance.
Relationship between mass and inertia
The larger the mass of the object, the greater the inertia.
Definition of mass
Mass is the property of an object which resists change in its motion.
Definition of weight
Weight is the force experienced by a mass in a gravitational field.
SI unit of mass and weight
Mass: Kilogram(kg)
Weight: Newton(N)
Physical quantities of mass and weight
Mass: Scalar
Weight: Vector
Is the magnitude of mass fixed or variable?
Fixed
Is the magnitude of weight fixed or variable?
Variable, depends on gravitational field strength
Definition of apparent weight
Refers to the reading shown on a measuring instrument
Definition of weightlessness
Weightlessness refers to a sensation whereby we do not experience contact forces and it does not mean that there is no weight acting on us.
What are the forces acting on the object during weightlessness?
No other forces other than the weight
Definition of Newton’s 3rd law
Newton’s third law states that the forces of action and reaction between interacting objects are equal in magnitude but opposite in direction, of the same type and act on opposite bodies.
Definition of linear momentum
Linear momentum is the product of the object’s mass and its linear velocity.
Formula of linear momentum and what does it mean?
p = mv
The faster the object is moving or the more mass it possesses, the greater the momentum it has in the direction of motion.
What physical quantity is linear momentum?
Vector
What is the direction of linear momentum?
Its direction is the same as its velocity.
Definition of resultant force
Resultant force is the rate of change of momentum it imparts on an object.
Definition of Newton’s 2nd law
Newton’s second law states that the rate of change of momentum of an object is proportional to the resultant force acting on it and occurs in the direction of the resultant force.
Formula of resultant force
Fr = dp/dt or Fr = ma or Fr = v* dm/dt
What does the area under a force-time graph represent?
Impulse
Should you use Fr = ma for A Level?
No, its a derived equation. It is only applicable when the mass is constant.
What does the gradient of a momentum-time graph represent?
Force
Definition of impulse
Impulse(of a constant force) is the product of the force and the time of the impact.
Unit for impulse
N s or kg m s^-1
Formula of impulse
Impulse = Fr x t
Impulse = Change in Momentum = mv - mu
Definition of the principle of conservation of linear momentum
The principle of conservation of linear momentum states that the total momentum of a system of interacting objects remains constant provided no external resultant force acts on the system.
Definition of inelastic collision
Inelastic collision is a collision in which the total momentum of colliding objects is conserved while its total kinetic energy is not observed.
Formula of the principle of conservation of linear momentum
Total momentum before interaction = Total momentum after interaction
m1u1 + m2u2 = m1v1 + m2v2
What happens when the total momentum remains the same after a collision?
There is a transfer of momentum.
Definition of perfectly inelastic collision
Perfectly inelastic collision is a special case of inelastic collision whereby two objects collide, stick together and then move on together with the same velocity after the collision.
Formula of perfectly inelastic collision
Total momentum before collision = Total momentum after collision
m1u1 + m2u2 = (m1 + m2)v
If there is a change in kinetic energy, what collision is it?
Inelastic collision
Definition of elastic collision
Elastic collision is a collision in which both the total momentum and total kinetic energy of the colliding objects are conserved.
What are the formulas of (perfectly) elastic collision?
Conservation of total momentum: m1u1 + m2u2 = m1v1 + m2v2
Relative speed = u1 - u2 = v2 - v1
Definition of superelastic collision
This refers to interactions whereby the total kinetic energy of the objects after the interaction is greater than the objects before.
Is the conservation of momentum used for superelastic collision?
Yes
Is the conservation of momentum used for elastic collision?
Yes
Is the conservation of momentum used for inelastic collision?
Yes
Is the conservation of momentum used for perfectly inelastic collision?
Yes
Is the conservation of kinetic energy used for superelastic collision?
No
Is the conservation of kinetic energy used for elastic collision?
Yes
Is the conservation of kinetic energy used for inelastic collision?
No
Is the conservation of kinetic energy used for perfectly inelastic collision?
No
Do objects move together or are separated after a superelastic collision?
They are separated
Do objects move together or are separated after an elastic collision?
They are separated
Do objects move together or are separated after an inelastic collision?
They are separated.
Do objects move together or are separated after a perfectly inelastic collision?
They move together.
