Dynamics Test Flashcards
Mass
the amount of matter in an object
-a SCALAR quantity
-units are kg
symbol m
Weight
the force of gravity on an object
- a VECTOR quantity
- units are N
- Fg
Force
a push or a pull
-a VECTOR quantity
F = ma
Newton
the SI unit for Force
Inertia
a property of matter that causes an object to resist changes in its state of motion
(it is directly proportional to the mass of the object
Kinetic Friction
the force that acts between moving surfaces
in a situation of kinetic friction, the force of static friction is not able to balance the applied force, so motion occurs
Static Friction
the force that prevents an object at rest from starting to move
Friction Comparison: Static & Kinetic
the magnitude of the force of Fk is NEVER GREATER than the maximum of the force of Fs
μk < μs
Friction
a force that is present in almost all-real life situations, in which it acts parallel to the common surface between 2 objects, resisting between them
Coefficient of Static Friction
Fs ≤ μsFN
μs = use when object is at rest
—> where μs is a proportionality constant
Coefficient of Kinetic Friction
Fk = μkFN
μk = use when object is sliding
—> where μk is a proportionality constant
What are the 4 Fundamental Forces?
- Gravitational Force
- Electromagnetic Force
- Strong Nuclear Force
- Weak Nuclear Force
Gravitational Force
- known as “force of gravity” or “weight”
- attraction ONLY
- acts between all objects in the universe
- weak force but long range
Electromagnetic Force
- caused by electrical charges
- most common force (light, electricity)
- strong force and long range
Strong Nuclear Force
- holds protons and neutrons together
- strongest force but very short range
Weak Nuclear Force
- responsible for radioactivity
- strong force but very short range
The mass and weight of a person are measured on Earth and then on Mars. How will the values of mass and weight for the person compare at the 2 locations?
The mass on Mars will be the same as on Earth, but the weight will be less. Mars is not as massive as the Earth, therefore, Fg will be smaller.
Newton’s First Law of Motion
An object at rest will stay at rest unless acted on by an unbalanced force
An object in motion will continue with constant speed and direction unless acted on by an unbalanced force
EX. a soccer ball is sitting at rest. it takes an unbalanced for of a kick to change its motion
A marble, a golf ball, and a bowling are all dropped off of the roof of the school at the exact same time. The three objects have different masses. The marble is the least massive; the bowling ball has the most mass. Which will reach the ground first?
All three will reach the ground at the same time. The gravitational force (or weight) of all three is different, but the acceleration is the same.
Newton’s Second Law of Motion
an object accelerates relative to the force applied and in the direction of the force
(the greater the force applied, the greater the distance travelled and the higher the speed)
- the acceleration is directly proportional to the net force, but is inversely proportional to the mass
EX. a tennis player hitting a tennis ball
Newton’s Third Law of Motion
For every force exerted by one object onto a second object, there is a force exerted by the second object onto the first that is equal in magnitude but opposite in directions. (action/reaction forces)
FOR EVERY ACTION, THERE IS AN EQUAL BUT OPPOSITE REACTION
EX. when the air from a balloon is released the air rushes downwards as the balloon is forced upwards
In order to understand Newton’s 3rd Law, you must understand Action-Reaction pairs. Based on the definition of these force pairs why don’t they cancel each other out on a FBD?
An FBD only shows forces that act on one object. Action-Reaction forces act on different objects.
1st Law of Motion Examples:
Inertia of a passenger makes her feel like she is being thrown ________________________ when the direction of the acceleration of the bus is opposite to the direction of its velocity.
FORWARD
1st Law of Motion Examples:
Inertia of a passenger makes her feel like she is being pushed _______________________ when the acceleration of the vehicle is in the same direction as its velocity.
BACKWARD
1st Law of Motion Examples:
What happens to the motion of the passenger when the bus goes around a curve?
Inertia of passenger makes her feel like she is being thrown inward or outward (depending on the direction of the curve) when the direction of the velocity changes as the vehicle accelerates around a curve
