Quick Review Flashcards - Click to flip and test your knowledge!
Question
What are the two primary effects a force can produce when applied to a body?
Answer
It can change the state of motion or change the size/shape (dimensions) of the body.
Question
How is a 'contact force' defined?
Answer
A force applied to a body by making physical contact with it.
Question
List three examples of contact forces mentioned in the text.
Answer
Frictional force, normal reaction force, and tension force.
Question
In what direction does the frictional force always act relative to the motion of a body?
Answer
In the direction opposite to the motion of the body.
Question
What is the 'normal reaction force' when a body is placed on a surface?
Answer
The equal and opposite force exerted by the surface upwards normal to itself.
Question
Where does the tension force develop when a body is suspended by a string?
Answer
In the string, acting towards the point of support.
Question
What is 'restoring force' in the context of a spring?
Answer
The force that tends to bring a stretched or compressed spring back to its original form.
Question
What term is used for forces experienced by bodies even without physical contact?
Answer
Non-contact forces (or forces at a distance).
Question
List the three types of non-contact forces described in the source material.
Answer
Gravitational force, electrostatic force, and magnetic force.
Question
How does the magnitude of a non-contact force relate to the distance $r$ between two bodies?
Answer
It varies inversely as the square of the distance ($F \propto \frac{1}{r^2}$).
Question
Which non-contact force is always attractive in nature?
Answer
Gravitational force.
Question
State the qualitative definition of force derived from Newton's First Law.
Answer
Force is an external cause which changes (or tends to change) the state of rest or motion of an object.
Question
Newton's First Law is also known as _____ Law of Inertia.
Answer
Galileo's
Question
What is 'inertia'?
Answer
The inherent property of an object by virtue of which it tends to retain its state of rest or of motion.
Question
What physical quantity is a measure of a body's inertia?
Answer
Mass.
Question
Why does a passenger standing in a train fall backwards when the train suddenly starts moving?
Answer
The lower body moves with the train while the upper body remains at rest due to inertia of rest.
Question
Why does a ball thrown vertically upwards by a person in a moving train return to their hand?
Answer
The ball remains in the same state of forward motion as the person and the train due to inertia.
Question
Formula: Linear momentum ($p$)
Answer
$p = m v$
Question
What is the SI unit of linear momentum?
Answer
$kg \cdot m \cdot s^{-1}$
Question
According to Newton's Second Law, the rate of change of momentum is directly proportional to the _____.
Answer
Applied force
Question
Formula: Mathematical expression of Newton's Second Law of motion
Answer
$F = m a$
Question
Define 'one Newton' of force.
Answer
The force which, acting on a mass of $1 kg$, produces an acceleration of $1 m \cdot s^{-2}$.
Question
What is the CGS unit of force?
Answer
Dyne.
Question
Relationship: How many dynes are in one Newton ($N$)?
Answer
$10^5 \text{ dyne}$
Question
Under what two conditions is the relation $F = m \frac{\Delta v}{\Delta t} = ma$ valid?
Answer
When velocities are much smaller than the speed of light and mass remains constant.
Question
How is Newton's First Law obtained from the Second Law mathematically?
Answer
By setting $F = 0$, which implies $a = 0$, meaning the body maintains its state of motion.
Question
Why does a cricketer pull their hands back while catching a fast-moving cricket ball?
Answer
To increase the time taken to stop the ball, thereby reducing the force exerted on the hands.
Question
Why do glass vessels break when falling on a hard floor but not on a carpet?
Answer
The carpet increases the time of impact, which decreases the force exerted on the vessel.
Question
State Newton's Third Law of motion.
Answer
To every action there is always an equal and opposite reaction.
Question
Do action and reaction forces act on the same body?
Answer
No, they always act simultaneously on two different bodies.
Question
How does Newton's Third Law explain the motion of a rocket?
Answer
The rocket exerts a force on gases (action), and the gases exert an equal and opposite force on the rocket (reaction).
Question
Why does a gun recoil when a bullet is fired?
Answer
The gun exerts a force on the bullet (action), and the bullet exerts an equal and opposite reaction force on the gun.
Question
Formula: Newton's Universal Law of Gravitation
Answer
$F = G \frac{m_1 m_2}{r^2}$
Question
What is the SI unit of the Universal Gravitational Constant ($G$)?
Answer
$N \cdot m^2 \cdot kg^{-2}$
Question
What is the numerical value of $G$ in SI units?
Answer
$6.67 \times 10^{-11} N \cdot m^2 \cdot kg^{-2}$
Question
Define 'force due to gravity' (Weight).
Answer
The force with which the Earth attracts a body towards its centre.
Question
Formula: Acceleration due to gravity ($g$) in terms of Earth's mass ($M$) and radius ($R$)
Answer
$g = \frac{GM}{R^2}$
Question
What is the average value of $g$ on the Earth's surface?
Answer
$9.8 m \cdot s^{-2}$
Question
How does the value of $g$ change as one moves from the equator to the poles?
Answer
It increases (it is slightly less at the equator than at the poles).
Question
What is the value of $g$ at the centre of the Earth?
Answer
Zero.
Question
How does the value of $g$ on the Moon's surface compare to that on Earth?
Answer
It is nearly one-sixth the value of $g$ on Earth.
Question
Process: For a body falling freely from rest, what is the formula for final velocity $v$ after time $t$?
Answer
$v = gt$
Question
Process: For a body thrown vertically upwards, what is the value of acceleration $a$?
Answer
$a = -g$
Question
What is the final velocity of a body when it reaches its maximum height after being thrown upwards?
Answer
Zero.
Question
Define 'mass' as described in the source material.
Answer
The quantity of matter a body contains.
Question
Is mass a scalar or a vector quantity?
Answer
Scalar quantity.
Question
Does the mass of a body change when its location changes?
Answer
No, it remains constant for a given body at rest.
Question
What is 'weight'?
Answer
The force with which the Earth attracts a body towards its centre ($W = mg$).
Question
Is weight a scalar or a vector quantity?
Answer
Vector quantity.
Question
Why does the weight of a body vary from place to place on Earth?
Answer
Because the value of $g$ varies from place to place.
Question
What is the SI unit of weight?
Answer
Newton ($N$).
Question
What is the gravitational unit of force in the M.K.S. system?
Answer
Kilogram force ($kgf$).
Question
Relationship: Define $1 kgf$ in terms of Newtons.
Answer
$1 kgf = 9.8 N$
Question
Which instrument is used to measure the weight of a body directly in Newtons?
Answer
A spring balance.
Question
What is the CGS gravitational unit of force?
Answer
Gram force ($gf$).
Question
How does the 'inertia of motion' differ from 'inertia of rest'?
Answer
Inertia of rest resists moving from rest, while inertia of motion resists changing speed or direction of existing motion.
Question
Concept: Free fall
Answer
Definition: The motion of a body falling from a height towards the Earth solely under the influence of gravity.
Question
According to the inverse square law, if the separation between two bodies is doubled, the force between them becomes _____.
Answer
One-fourth
Question
Why do dust particles fall out of a hanging carpet when it is beaten with a stick?
Answer
The carpet moves forward while the dust particles stay in position due to inertia of rest.