Forces
More About Forces
Newton's 1st & 2nd Laws
Newton's 3rd Law
Review
100
What is a force?
A push or a pull
100
What is fluid friction?
The friction that opposes an object moving through a liquid or a gas.
100
Newton’s 1st Law is also known as the law of ________
Newton’s 1st Law is also known as the Law of Intertia
100
According to Newton’s 3rd Law of motion, forces always exist in _____
According to Newton’s 3rd Law of motion, forces always exist in pairs (action/reaction).
100
On a distance-time graph, the slope of the line indicates what?
Speed
200
An object accelerates (moves) in the same direction as...
An object accelerates in the same direction as the net force
200
How is Net Force calculated?
By adding forces that act in the same direction and subtracting forces that act in opposite directions.
200
According to Newton’s 2nd Law, how can one determine an object’s acceleration?
acceleration=force/mass
200
Finish this statement: Whenever one object exerts a force on a second object, the second object exerts a force on the first object that is…
Whenever one object exerts a force on a second object, the second object exerts a force on the first object that is… equal in size and opposite in direction.
200
What is the difference between speed and velocity?
Speed is calculated by dividing the distance traveled by the time it took to travel that distance. Velocity also includes direction.
300
What happens when an unbalanced force acts on an object?
The object accelerates (moves)
300
Put the 4 types of friction in order from weakest to strongest
Fluid, Rolling, Sliding, Static
300
According to Newton’s 1st Law, what happens when the net force acting on an object is zero?
There is no change in the object’s motion (an object at rest will stay at rest, while an object in motion will continue at the same velocity (speed and direction).
300
Define momentum
The product of an object’s mass and its velocity. (p=m*v)
300
FREE!
FREE!
400
You are helping your friend rearrange the furniture in her bedroom. She wants to switch the positions of her dresser and her desk (the desk has wheels). Which would be easier to move and why?
The desk with wheels is easier to move, because rolling friction is less than sliding friction.
400
The force that pulls (attracts) objects toward each other (even if we don't feel it) is called...
Gravity
400
What is weight?
The force of gravity acting on an object which depends on its mass.
400
Explain how Newton’s 3rd Law of motion is at work when comparing the forces of a person walking versus a person running.
In both cases, the foot pushes off against the ground (action force) and the ground pushes back with an equal and opposite reaction force, propelling the person forward. A runner would have more action force, so the equal reaction force would be greater, pushing the runner farther.
400
What are the three ways an object can accelerate?
1. Change in speed 2. Change in direction 3. Change in both.
500
What is the net force acting on a stationary (not moving) object?
0 N
500
A bowling ball and a golf ball are dropped off a cliff. Which will reach terminal velocity faster? Explain.
The golf ball will reach terminal velocity faster, because the greater mass of the bowling ball means it has a greater gravitational force acting on it, so it will take longer for the air resistance to equal the gravity.
500
A box has a mass of 150kg. If a net force of 3000N acts on the box, what is the box’s acceleration?
acceleration=force/mass acceleration=3000N/150kg acceleration=20m/s/s
500
Explain how momentum is conserved in a closed system.
Since no force enters or leaves the system, the momentum of one object in motion can transfer to the other object(s) in the system. The total momentum remains the same, while the loss of momentum in one object becomes the gain of momentum in the other.
500
A car traveling at a speed of 25 m/s increases its speed to 30 m/s in 10 seconds. What is its acceleration?
acceleration=(FV-IV)/Time acceleration=(30m/s-25m/s)/10 acceleration=5m/s/10 acceleration=0.5m/s/s
M
e
n
u