Inertia & Forces
What is inertia?
The tendency of an object to resist changes to its motion.
State Newton’s First Law.
Objects stay at rest or move at constant velocity unless acted on by an unbalanced force.
What does a free body diagram show?
All forces acting on an object.
What is a two-body problem?
A problem involving two connected objects experiencing forces.
Define a projectile.
An object moving through the air only under gravity (no thrust).
Is a book sitting on a table an example of balanced or unbalanced forces?
Balanced forces.
What is Newton’s Second Law as a formula?
F=ma
A 10 N rightward force and a 10 N leftward force act on an object. What is the net force?
0 N
Why is treating two objects as one useful?
It simplifies finding total acceleration.
A ball is launched horizontally. What is its initial vertical velocity?
0 m/s.
A car suddenly stops and you lurch forward. Which law does this describe?
Newton’s First Law (inertia).
If you double the force on an object, what happens to acceleration?
It doubles.
Draw or describe the FBD for a book sliding right with friction.
Forces: gravity down, normal up, applied right, friction left.
Two boxes (3 kg and 5 kg) pulled with 16 N. Find acceleration (treat as one).
Total mass 8 kg → a=2m/s^2
Solve for time: A projectile falls 20 m.
Use d=1/2 g^2 -> t = 2.0s
Define force.
A push or pull that can change an object’s motion.
State Newton’s Third Law.
For every action, there is an equal and opposite reaction.
An object has 50 N right and 20 N left. What is the acceleration if the mass is 5 kg?
Net force = 30 N, a = 6 m/s^2
In a two-body system, tension is the same on both objects if the rope is…
Massless and frictionless.
A ball is kicked at 12 m/s horizontally. How far does it travel in 3 seconds?
36 m.
Identify two forces acting on a box sliding across the floor.
Gravity, normal force, friction, applied force (any two).
Give a real-world example of Newton’s Third Law.
A rocket pushing exhaust gases downward produces upward thrust.
Determine the net force on an object with forces: 10 N up, 6 N down, 5 N right, 5 N left.
4 N upward.
Combine individual forces: Box A pulled right with 20 N, friction 4 N; Box B pulled right with 15 N, friction 5 N. Find total net force.
(20−4)+(15−5)=26 N right.
A projectile is launched up with 15 m/s. How long until it reaches the top?
t=v/g≈1.53 s.