Constant Velocity and Newton’s First Law (Law of Inertia)
When the net Force is zero, there is no acceleration and the velocity remains constant (either 0 or some constant positive/negative value).
Find Newton’s First Law of Motion and write it down:
Newton's 1st Law:
If ΣF = 0, then ∆v = 0,
Which page(s) of the textbook did you use? __ __
AND if ∆v = 0, then Σ F = 0
-The Energy stored in EK is constant.
In other words, unless there is a NET FORCE on the object its VELOCITY will not change. If it is initially at rest, it will
___________________________________________________; if it is moving at certain velocity, it will continue
_______________________________ ____ ____________________________ .
TRUE OR FALSE:
a. No force is required to keep an object moving.
b. A vehicle moving at a constant velocity of 40 km/h will change its stored Kinetic Energy as time goes by.
Common Forces and Force Diagrams:
Fgravitation
The mass of an object tells us how much it resists to a change in motion or inertia. It is measured in kilograms (kg).
The gravitational force on a mass is called Weight (W=mass x gravity) and it is measured in newtons (N).
For example: A woman has a mass of 50kg. What is her weight in newtons?
2
2
Gravity is 9.8 m/s . For convenience, we will approximate it to 10 m/s .
FNormal
Is the force of support; the table supports the weight of the object. Normal means perpendicular to the surface.
Example-1: A large bowling ball has a mass of 2 kg. Determine the normal force.
1. Diagram:
2. Fgravity=2 x 10 =20 Newtons
|FNormal|= |Fgravity | because it is not moving up nor down.
3.
Draw FNormal and determine the value of FNormal.
Example-2: An carriage is pulled by a horse at constant velocity.
1. Is there a net force?
2. Label FNormal and Fgravity.
FPull
The force applied to break inertia will counter the force of friction (Ffriction).
Ffriction
The interaction between the two surfaces’ molecules.
Ffriction = µ x |FNormal |
At constant velocity; |Ffriction|= | FPull |
1.
Use the diagram above. If all forces are balanced; which forces would have equal magnitude and opposite directions?
2.
If the carriage had less mass, were lighter; which forces would be smaller in magnitude?
3.
How does the normal force change if one pushed down on this carriage by adding weight?
4.
How would the normal force change if we emptied the carriage?
Example-3: A bowling ball is released and starts traveling at constant velocity on a slippery surface.
1.
Sketch a point diagram for the forces acting on the
just after it is released from the hand.
2.
Which forces are not in balance?
3.
Which forces are in balance?
bowling ball
Example-4: A metal crate is unloaded into a slippery floor at Home Depot. As it was put onto the floor, it got a slight push and
started to slide over the floor at constant velocity. We will analyze the forces on the sliding crate.
Sketch and label the forces acting on the moving crate.
Example-5: The same situation as Example-4, but this time the crate
for 11 seconds, slowing down, and eventually stops.
1.
Which force is acting to make it stop?___________
2.
Which force is acting to make it stop?___________
slides
Balanced Forces and Newton’s Third Law (Action-Reaction Principle)
Find Newton’s Third Law and write it down:
Which page(s) of the textbook did you use? __ __
Newton's 3rd Law:
Interacting forces between two objects are equal in strength but in opposite direction.
In other words, forces arise from the interaction between different objects. If object-A exerts a force on object-B, then object-B
exerts a …………….. on object-A, of ……………………..magnitude but of ……………………….direction.
TRUE OR FALSE:
a. The normal force is a support reaction to the weight of on abject.
b. A scale measures your Mass.
c. A scale measures your FGrav
d. A scale measures the Normal force (FN).