About Newton’s Laws, Gravity, and Motion
Q1: What is inertia?
Inertia is the property of an object to resist changes in its state of motion. This means that an object at rest will stay at rest, and an object in motion will continue moving at a constant velocity unless acted upon by an external force.
Q2: Why does a cricketer pull his hand back while catching a fast-moving ball?
By pulling his hands back, the cricketer increases the time over which the ball’s momentum is brought to zero. This reduces the average force exerted on his hands, making the catch more comfortable and reducing the risk of injury.
Q3: Why does an athlete prefer to land on sand instead of a hard floor while taking a high jump?
Sand deforms and compresses upon impact, increasing the time over which the athlete’s momentum is reduced to zero. This reduces the average force exerted on the athlete’s body during landing, making it safer and lessening the likelihood of injury.
Q4: What is linear momentum and how is it related to Newton’s Second Law of Motion?
Linear momentum is the product of an object’s mass and velocity (\( p = m \cdot v \)). Newton’s Second Law can be expressed in terms of momentum: \( F = \frac{dp}{dt} \), indicating that the force applied to an object is equal to the rate of change of its momentum.
Q5: What is relative motion and absolute motion?
Relative motion refers to the motion of an object as observed from a particular frame of reference, meaning the perceived motion can vary based on the observer’s position and movement. Absolute motion is a theoretical concept of an object moving in a fixed, universal frame of reference, though in practical terms, all motion is relative.
Q6: Why does a stationary boat move away when you step ashore?
When you step off the boat, you exert a backward force on the boat (action), and the boat exerts an equal and opposite forward force on you (reaction). This reaction force causes the boat to move away from the shore.
Q7: Why do two spring balances joined at their free ends show the same reading when pulled apart?
When two spring balances are joined and pulled apart, they show the same reading because the forces involved are equal in magnitude and opposite in direction, according to Newton’s Third Law. The connection ensures that the force applied to one is transmitted directly to the other.
Q8: Why does a light ball rise upwards after striking the ground?
When a light ball strikes the ground, it exerts a downward force on the ground (action). According to Newton’s Third Law, the ground exerts an equal and opposite upward force on the ball (reaction), causing it to rise. Additionally, the ball’s elasticity helps it rebound.
Q9: Where is gravity stronger, at the equator or at the polar regions?
Gravity is slightly stronger at the polar regions than at the equator. This is due to the Earth’s shape (an oblate spheroid) and the centrifugal force caused by the Earth’s rotation, which is strongest at the equator and weakest at the poles.
Q10: How is the Universal Law of Gravitation connected to the force due to gravity?
The Universal Law of Gravitation, \( F = G \frac{M m}{r^2} \), describes the gravitational force between two masses. Near the Earth’s surface, this formula simplifies to \( F = m \cdot g \), where \( g \) is the gravitational acceleration, demonstrating how the universal law applies to specific scenarios like the force due to gravity at the Earth’s surface.
Q11: Why does gravity decrease as you move higher or toward the center of the Earth?
Gravity decreases with altitude because the distance from the Earth’s center increases, reducing the gravitational pull. It also decreases toward the center of the Earth because the effective mass beneath you decreases, as more of the Earth’s mass is above you, partially canceling out the gravitational force.