Newton’s Laws & Forces
Define Newton’s 1st Law in your own words.
An object at rest stays at rest and an object in motion stays in motion unless acted on by an unbalanced force.
What is the difference between a scalar and a vector? Give one example of each.
A scalar has magnitude only (e.g., speed, mass). A vector has magnitude and direction (e.g., velocity, displacement).
Define acceleration in terms of velocity and time.
Acceleration = change in velocity ÷ time (Δv/Δt).
Define projectile motion in simple terms.
Projectile motion = motion with a vertical acceleration due to gravity and independent horizontal motion (two components).
Define normal force.
Normal force = the contact force perpendicular to a surface that supports an object (balances gravity on flat surfaces).
A rock is being pushed and speeds up. According to Newton’s 3rd Law, how does the force you exert on the rock compare to the force the rock exerts on you?
The force you exert and the force the rock exerts on you are equal in size and opposite in direction(Newton’s 3rd Law).
What does multiplying a vector by cos θ give you?
Multiplying by cos θ gives the x-component of the vector.
Draw a graph that correctly shows the relationship between kinetic friction and normal force? (Friction increases linearly with normal force)
A linear graph where kinetic friction is directly proportional to the normal force (friction increases as normal force increases).
A ball is thrown horizontally from a cliff. Which two motions happen at the same time?
Horizontal motion at constant velocity and vertical motion with constant acceleration downward (gravity) occur simultaneously.
Which direction does kinetic friction act relative to an object’s motion?
Kinetic friction acts opposite the direction of motion.
If the net (total) force on a moving object is zero, what will happen to its motion?
It will keep moving at the same speed and direction (constant velocity).
What does displaement measure?
How far and in what direction an object is from its starting point?
Describe the motion represented by a horizontal line on a velocity-time graph.
A horizontal line on a velocity–time graph means constant velocity (zero acceleration).
Two objects drop from the same height at the same time — one is thrown horizontally, the other is simply dropped. Which hits the ground first?
They hit at the same time (vertical motion is the same).
If you double the normal force, what happens to the force of kinetic friction?
If the normal force doubles, kinetic friction (μ_k N) doubles (friction ∝ normal force).
What does it mean for an object to be in equilibrium?
An object is in equilibrium when the net force is zero (all forces cancel) — no acceleration.
Which trig function gives the x-component of a vector at angle θ above the x-axis?
Cosine: Vx=Vcosθ.
What does a horizontal (flat) line on a velocity–time graph tell you about motion?
Velocity is constant (acceleration = 0).
If you double the horizontal launch speed of a projectile (same height), what happens to its horizontal distance (range)?
The horizontal distance doubles (time in air is the same, range = vx×t).
A book rests motionless on a table. What two forces are balanced to keep it in equilibrium?
Gravity (weight) downward and the normal force upward are balanced.
Two ice skaters push off each other. One skater is much lighter. Which skater will have the larger acceleration and why?
The lighter skater — same force causes a bigger acceleration on the smaller mass.
Whats the difference between speed and velocity?
Speed is how fast velocity is how fast and in what direction.
If an object has a positive acceleration, what happens to its velocity?
The object’s velocity increases in the positive direction.
In horizontal projectile motion (no air), does the horizontal speed change while the object is in the air?
No — horizontal speed stays constant (no horizontal acceleration).
Give one real-life example of static friction and one of kinetic friction.
Static friction example: a heavy box that doesn’t move when you push; Kinetic friction example: sliding a book across a table.