Types of Forces
This force acts between surfaces and opposes their motion or attempted motion.
Friction
Two students push a desk with equal forces in opposite directions. The desk does not accelerate. What is the net force?
What is 0 N?
Balanced Forces
This property describes an object’s tendency to resist a change in its motion.
Inertia
What is the equation that relates net force, mass, and acceleration?
Force = Mass x acceleration
For every action force, there is a force of equal strength in the opposite direction. Which law is this?
Newton’s Third Law
A rolling suitcase’s wheels move across the floor. This type of friction acts between the wheels and the floor.
Rolling Friction
A dog pulls a toy to the right with 18 N while a person pulls it to the left with 7 N. Find the net force and its direction.
11 N to the right
A soccer ball remains at rest on the grass until it is kicked. Which law helps explain why its motion changes only when an unbalanced force acts?
Newton’s First Law
A net force of 24 N acts on a 6 kg cart. Calculate its acceleration.
4 m/s2
A swimmer pushes water backward with their hands(action) What is the reaction force?
The water pushing the swimmer forward
A 6 kg toolbox is on Earth. Calculate its weight.
- must include units for it to count
58.8 Newtons
A cyclist moves forward at a steady speed. The forward force is 120 N. What is the total backward force, and are the forces balanced or unbalanced?
120 N backward and balanced forces
When Net Force = 0 Newtons an objects speed is constant. or the object is not accelerating.
A book rests on a table. The forces on it are balanced. Describe its motion.
The book remains at rest
A 7 kg ball accelerates at 3 m/s2. Calculate the net force on it.
21 Newtons
A bird pushes air downward with its wings. Identify the reaction force.
The air pushing the bird upward
A 12 kg object is on a planet where gravitational field strength (g) is 4 N/kg. Calculate its weight there and on Earth.
48 N on that planet and 117.6 N on Earth
A sled is pulled forward with 55 N. Friction acts backward with 20 N, and air resistance acts backward with 5 N. Find the net force and its direction.
30 N forward
A train travels in a straight line at constant speed. The forces on it are balanced. What would happen to its motion if the net force remains zero?
The train continues moving at the same speed in the same direction
The same net force acts on two carts. Cart A has a mass of 5 kg, and Cart B has a mass of 10 kg. How do their accelerations compare?
Cart A’s acceleration is twice Cart B’s acceleration, because doubling mass while keeping force the same halves acceleration
A skater pushes against a wall and rolls backward. Identify the two interacting objects and the force each exerts.
The skater pushing the wall and the wall pushing the skater backward with an equal force in the opposite direction
A 15 kg object weighs 180 N on a distant planet. Find the planet’s gravitational field strength (W = m x g - solve for g) . Then determine the object’s weight on Earth.
12 N/kg for the planet’s gravitational field strength and 147 N for its weight on Earth
A cart moves to the right. A student pushes right with 90 N while friction acts left with 35 N and another student pulls left with 25 N. Find the net force. If the leftward pull increases to 55 N, find the new net force and direction.
30 N to the right at first, then 0 N after the pull increases
A bus stops suddenly, and standing passengers lurch forward. Use inertia and Newton’s First Law to explain why.
The passengers’ bodies tend to keep moving forward when the bus stops, unless an unbalanced force changes their motion
A 4 kg cart accelerates at 3 m/s2. The same net force is then applied to an 8 kg cart. Find the force and the second cart’s acceleration
What are 12 N and 1.5 m/s2
A small rolling cart collides with a larger stationary cart. Compare the force each cart exerts on the other during the collision, and explain why their motions may change by different amounts.
Each cart exerts an equal-strength force in the opposite direction on the other, but their accelerations may differ because their masses differ