Ch. 4 (Midterm) Flashcards
(27 cards)
Force
something with the capability to cause change in a motion of a system
- pull or push
Properties of Force (5)
Direction Orientation Magnitude Point of Application Line of Action
Newton’s First Law
Law of Inertia
-An object at rest stays at rest. An object in motion stays in motion with the same speed and direction unless acted upon by an unbalanced force
Newton’s Second Law
Law of Acceleration
The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.
-change in motion is directly proportional to the magnitude of the applied force
Newton’s Third Law
Law of Action-Reaction
To every action there is always opposed and equal reaction
-forces exist in pairs
Law of Attraction
Every body in the universe attracts every other body because of gravitational force due to the size of the body’s masses
- the greater the mass, the greater the attraction
- the less mass, the less attraction
- the interaction of objects even when they are not in contact (action-at-a-distance).
- i.e. force of gravity from Earth on humans
Types of Forces (6)
Non-Contact (Field) Forces Contact Forces External Forces Internal Forces Action Forces Reaction Forces
Field and Field-Force
Field: any object possessing mass creates an invisible field of influence stretching throughout space
-i.e. force between the moon and the Earth
Field-Force: non-contact force
-i.e. Newton’s gravitational attraction
Non-Contact (Field) Forces (4)
Strong nuclear force
Electromagnetic force
Weak nuclear force
Gravitational force
Strong Nuclear Force
occurs between subatomic particles; prevent the nucleus of an atom from exploding because of the repulsive electric force produced by its protons
Electromagnetic Force
between electric charges
Weak Nuclear Force
a product of some radioactive decay process, which plays an important part in the nuclear reactions by which the sun produces energy
Gravitational Force
exists between bodies of mass
Contact Forces
the result of physical contact between two bodies
-i.e. jumping; baseball and bat
External Forces
interact with the system from the outside.
- i.e. gravity, external movement environment
- only external forces can change MOTION of system (Newton’s First Law of Motion)
Internal Forces
act within the defined system.
i. e. muscles forces, internal to the system
- only internal forces can change SHAPE of the system
Action Forces
“the force”
- the initially applied force
- i.e. the force on the floor by a person when standing
Reaction Force
the simultaneous equal counterforce acting in the opposite direction to the action force
-i.e. the force on the person by the floor when standing
Friction
Force that resists the sliding of two objects in contact
Normal Force
force that acts downward on one surface and upward on another
-i.e. force between foot and ground when walking (downward on the ground, upward on your foot)
Static Friction
exists when two contacting surfaces are not currently sliding relative to each other but do possess the potential for movement
-i.e. moving a heavy block.
-Initially force: box doesn’t move, static friction > applied force
-Gradually apply greater amounts of force until box moves:
static friction < applied force
Kinetic Friction
friction that occurs when two surfaces are already sliding relative to each other
- it’s easier to maintain the sliding of an object once it has begun moving
- i.e. sliding a box across the floor
Rolling Friction
exists whenever one surface is rolling over another but not sliding
- depends of a coefficient of friction and normal force
- i.e. car tires when driving
Pressure
the magnitude of applied force acting over a given area
P=F/A
