Show:
inertia
force and acceleration
action and reaction
friction and gravity
balanced vs unbalanced forces
100

What is inertia?

  • Answer: Inertia is the fundamental property of matter that describes an object's tendency to resist any change in its state of motion (either staying at rest or continuing in uniform motion)
100

Conceptual Question: Relationship between force, mass, and acceleration

Force is directly proportional to mass and acceleration

100

What does Newton's Third Law of Motion state?


Answer: For every action, there is an equal and opposite reaction. This means that forces always occur in pairs; when one object exerts a force on a second object, the second object simultaneously exerts a force equal in magnitude and opposite in direction on the first object.

100

Why does a feather fall slower than a bowling ball if gravity pulls them equally?


  • A: Gravity accelerates all objects at the same rate (approx. 9.8 m/s² on Earth), but air resistance (a form of friction) affects the feather more significantly due to its large surface area and low mass, slowing its descent.
100
  1. What is the main difference between balanced and unbalanced forces?
  • A: Balanced forces are equal in magnitude and opposite in direction, resulting in no change in an object's motion (net force is zero), whereas unbalanced forces are unequal, causing a change in motion (acceleration).
200

 What quantity determines an object's inertia?

  • Answer: An object's mass. More mass means more inertia, making it harder to start or stop the object.
200

Conceptual Question: Effect of constant force on acceleration 



Applying a constant net force to an object results in a constant acceleration in the direction of the force, according to 

a=F/mbold a equals bold cap F / m
200

Why don't action and reaction forces cancel each other out, causing all motion to be impossible?

 

Answer: Action and reaction forces do not cancel each other because they act on different objects. For motion to occur, there must be a net force on a single object. For example, when a person walks, they push backward on the ground (action), and the ground pushes forward on them (reaction). The reaction force on the person causes them to accelerate forward.

200

How does friction help us walk?

  • A: Friction between your shoes and the ground pushes backward as your foot pushes backward, propelling you forward; without it, your feet would slip, and you couldn't move.
200

What happens to an object when balanced forces act on it?

  • A: Its state of motion doesn't change; if it's at rest, it stays at rest, and if it's moving, it continues at a constant velocity (speed and direction).
300

Why do you feel thrown forward when a car suddenly brakes? 

  • Answer: Your body has inertia and wants to keep moving forward at the car's original speed, even as the car slows down, causing you to lurch forward.
300

Procedural Question: Calculate acceleration 

The acceleration of the mass is 



5m/s25 space bold m / bold s squared


300

 When a rocket launches, what are the action and reaction forces?


Answer:

  • Action Force: The rocket engines push hot exhaust gases downward and backward.
  • Reaction Force: The exhaust gases push the rocket upward and forward, propelling it into space. This principle works even in a vacuum.
300

What is the difference between mass and weight?


  • A: Mass is the amount of matter in an object (e.g., 10 kg), which stays the same everywhere, while weight is the force of gravity on that mass (mass x gravity), so your weight changes on the Moon but your mass doesn't.
300

Give an example of balanced forces.

  • A: A book resting on a table, where gravity pulling it down is balanced by the normal force from the table pushing up, or a tug-of-war with equal strength teams.
400

Is inertia only for moving objects?

  • Answer: No, it applies to both. Objects at rest have "inertia of rest" (they resist starting to move), and objects in motion have "inertia of motion" (they resist stopping or changing direction).
400

Calculate required force 

The required force is 

. 


6N6 space bold cap N
400

Identify the action-reaction pair when a book is resting on a table. 


Answer:

  • Action Force: The book exerts a downward force (its weight due to gravity) on the table.
  • Reaction Force: The table simultaneously exerts an equal and opposite upward force (normal force) on the book, which keeps the book at rest.
400

What factors affect the force of gravity between two objects?

  • A: The force of gravity depends on the mass of the two objects (more mass means more gravity) and the distance between them (greater distance means less gravity).
400

Give an example of unbalanced forces.

  • A: A car speeding up, a ball falling from a tree, or a person pushing a stalled car to get it moving.
500

What famous law is also known as the Law of Inertia? 

  • Answer: Newton's First Law of Motion.
500

 Calculate acceleration with friction 

The acceleration of the box is 

3m/s23 space bold m / bold s squared
500

When a large Mack truck and a small Honda Civic have a head-on collision, on which vehicle is the impact force greater?


Answer: The impact force is exactly the same for both vehicles. According to Newton's Third Law, the force the truck exerts on the Civic is equal in magnitude to the force the Civic exerts on the truck. However, the smaller Civic experiences a much greater acceleration and change in motion because it has significantly less mass (Newton's Second Law: Force = Mass x Acceleration).

500

What is the role of normal force in friction?

  • A: The normal force (the force pushing surfaces together, often equal to weight on a flat surface) directly increases friction; if you push down harder on a book sliding on a table, you increase the normal force, making it harder to push (more friction).
500

What is the net force on an object experiencing balanced forces?

  • A: The net force is zero, as the forces cancel each other out.