May the Force Be With You
What is a force?
A push or pull on an object.
A box has 25 N pushing right and 25 N pushing left. Are the forces balanced or unbalanced?
Balanced
A soccer ball stays still until someone kicks it. Which Newton’s Law does this demonstrate?
Newton's 1st Law
What force pulls objects toward Earth?
Gravitational
What equation is used to calculate force?
F = m x a
Is friction a contact or non-contact force?
Contact force
A tug-of-war team pulls with 60 N to the left, while the other team pulls with 45 N to the right. What is the net force and direction?
15 N to the left
Which Newton’s Law is represented by F = ma?
Newton's 2nd Law
What force opposes motion when two surfaces rub against each other?
Frictional
A 5 kg object accelerates at 2 m/s². What is the force?
10 N
A ball is dropped from a balcony. What force causes it to accelerate toward the ground?
Gravitational Force
Three forces act on a cart: 50 N right, 20 N left, and 15 N left. What is the net force, and are the forces balanced or unbalanced?
15 N to the right; unbalanced
When you jump, you push down on Earth and Earth pushes you upward. Which Newton’s Law explains this?
Newton's 3rd Law
A person stands still on the floor. Two vertical forces act on the person. Identify both forces and their directions.
Gravitational force acts downward, and normal force acts upward.
A 6 kg object experiences a net force of 24 N. What is its acceleration?
4 m/s²
A book is sitting on a table. Gravity pulls it downward, but it does not fall. What upward force balances gravity?
Normal
Can an object be moving even if the forces acting on it are balanced?
Yes. It can move at a constant speed in a straight line when the net force is 0 N.
A loaded shopping cart and an empty shopping cart are pushed with the same force. Which accelerates more, and why?
The empty cart because it has less mass; according to Newton’s 2nd Law, less mass produces greater acceleration for the same net force.
A sled is being pulled across snowy ground by a rope. Name the force from the rope and the force that opposes the sled’s motion.
Tension force and frictional force
A 12 kg object accelerates from rest at 2.5 m/s². What is the net force?
30 N
A hockey puck slides across ice and eventually stops. If objects tend to remain in motion, what force causes the puck to slow down?
Friction
A box has a net force of 0 N, but it is already moving. What will happen to its motion?
It will continue moving at a constant velocity unless an unbalanced force acts on it.
A student jumps off a small boat onto a dock. As the student moves forward toward the dock, the boat moves backward.
Newton’s Third Law. The student pushes backward on the boat, and the boat pushes forward on the student with an equal and opposite force.
A lamp hangs motionless from the ceiling by a cord. Gravity pulls down on the lamp with 50 N. If the forces are balanced, what is the tension force in the cord and in what direction does it act?
50 N Upward
A 20 kg cart is pushed with 100 N to the right while friction exerts 20 N to the left. What is the cart’s net force AND acceleration?
Net force = 100 N − 20 N = 80 N right
Acceleration = F ÷ m = 80 ÷ 20 = 4 m/s² to the right