Motion Matters
What does it mean for an object to be in motion?
Motion means an object’s position changes over time.
What is the formula for average velocity?
v=Δt / Δx
What does acceleration describe?
Acceleration describes how velocity changes over time. It can mean speeding up, slowing down, or changing direction.
What is a force?
A force is an interaction that can change an object's motion. Force is measured in Newtons (N).
Which Newton's Law says that an object will keep its current state of motion unless acted on by a net external force?
Newton's 1st Law — the Law of Inertia.
A football player moves from the 10-yard line to the 30-yard line. What has changed?
The player's position changed.
A football player runs 30 meters in 5 seconds. What is the player's average velocity?
6 m/s
A football player increases velocity from 2 m/s to 8 m/s in 3 seconds. What is the player's acceleration?
a = (8−2)/3 = 2 m/s2
What is the difference between a balanced force and an unbalanced force?
Balanced forces result in zero net force and no acceleration. Unbalanced forces result in a nonzero net force and acceleration.
Newton's 2nd Law is represented by what equation?
Fnet=ma
What two measurements do you need to describe how fast the player moved?
Distance and time.
What is the difference between speed and velocity?
Speed tells how fast something moves. Velocity tells how fast it moves and in what direction.
A player is moving at 10 m/s and slows to 4 m/s in 2 seconds. What is the player's acceleration?
a= (4−10) / 2 = −3 m/s2
A football player has 500 N of force acting forward and 300 N acting backward. What is the player's net force?
Fnet= 500−300 =200 N in the positive
A football player pushes backward against the ground while sprinting forward. Which Newton's Law explains why the ground pushes the player forward?
Newton's 3rd Law. The ground pushes forward on the player with a force equal in magnitude and opposite in direction to the player's backward force on the ground.
A player starts at the 20-meter mark and ends at the 50-meter mark. What is the player's displacement?
30 meters of displacement.
A player runs 20 m east in 4 s. What is the player's average velocity?
5 m/s east
A football player is running at a constant velocity of 8 m/s in a straight line. What is the player's acceleration?
Answer: 0 m/s². Constant velocity means velocity is not changing, so there is no acceleration.
A player is moving at a constant velocity in a straight line. What does this tell you about the net force acting on the player?
Answer: The net force must be 0 N because constant velocity means the player has no acceleration.
A 100 kg player and a 50 kg player experience the same net force. Which player has the greater acceleration, and why?
The 50 kg player has the greater acceleration because the same net force acting on a smaller mass produces greater acceleration.
Two football players both run for 5 seconds. Player A travels 20 m, while Player B travels 35 m. What can you conclude about their motion, and what additional information would you need to calculate each player's average velocity?
Player B traveled farther in the same amount of time, so B had a greater average speed.
To calculate average velocity, you need displacement and time (and direction if direction matters).
Player A runs 40 m in 5 s. Player B runs 30 m in 3 s. Which player has the greater average velocity, and by how much?
Player A: 40/5=8 m/s
Player B: 30/3=10 m/s
Player B has the greater average velocity by 2 m/s (assuming they are moving in the same direction).
Player A goes from 0 m/s to 6 m/s in 3 seconds. Player B goes from 4 m/s to 10 m/s in 2 seconds. Which player has the greater acceleration, and by how much?
Player A:
a= (6−0) / 3 = 2 m/s^2
Player B:
a= (10−4) / 2=3 m/s^2
Player B has the greater acceleration by 1 m/s².
A 90 kg football player accelerates at 2 m/s². What is the net force acting on the player, and what does that force tell you about the player's motion?
Fnet=ma= (90)(2) =180 N
The 180 N net force means the player is accelerating in the direction of the net force, so the player's velocity is changing.
Player A pushes Player B with 800 N of force. According to Newton's 3rd Law, what force does Player B exert on Player A? Explain why these forces do not cancel each other out.
Player B exerts 800 N on Player A in the opposite direction.
They do not cancel because the two forces act on different objects: one force acts on A, and the other acts on B.