Mechanics Exam 2

UARK

Linear Kinetics

The kinetics of particles, objects, or systems undergoing linear motion

Mass

the quantity of matter composing a body (kg)

Inertia

the natural tendency of a body to resist a change in its state of motion (measure of how difficult it is to change an objects velocity)

Center of Mass

the average location of the mass of an object

Force (include units)

a push or a pull exerted by objects on other objects (N)

What is the difference between internal and external forces?

External: forces that act on a “system” as a result of its interaction with the surrounding environment

Internal: forces that at within the “system” whose motion is being investigated

What is the difference between mass and weight?

mass is the quantity of (same no matter where)

weight is mass multiplied by acceleration due to gravity (environment dependent)

Newton’s First Law

Law of Inertia: Object in motion stays in motion, object at rest stays at rest unless acted upon by an external force

Newton’s Second Law

Acceleration: A force applied to a body causes acceleration of the body in the direction of the force, with a directly proportional magnitude and inversely proportional to the body’s mass (F=ma)

Newton’s Third Law

Action/Reaction: For every action there is an equal and opposite reaction (equal magnitude in opposite direction) forces come in pairs

What is the difference between contact and non-contact forces?

non-contact occurs when object is not touching another (gravity, air resistance)

contact forces occur when objects are touching each other (come in action/reaction pairs)

Friction

force that acts over the contact area between two bodies

Static Friction

objects do not slide relative to each other

equal in magnitude and opposite in direction to the sum of all other shear forces

Dynamic Friction

objects sliding relative to each other

sum of other shear forces exceeds the maximum static friction

Limiting Friction

maximum amount of friction that develops just before two surfaces begin to slide

Why is friction essential for human locomotion?

It provides the propulsive and breaking acceleration force

When would you want to minimize friction?

For activities like dance where you want more freedom of motion

How is friction changed when you push or pull object?

pull: upward component of force

push: downward component of force

How does the angle of a pull influence friction?

changes the weight of the normal force countering the weight (downward increases force upward decreases force)

Why does surface area NOT influence friction?

larger contact area reduces pressure offsetting the increased area for friction

What is the impulse-momentum relationship?

when impulse acts on the system there is a change in the system’s momentum. The average net force acting over some interval of time will cause a change in momentum of an object

How does impact time affect applied force when speeding up and when slowing down? (use impulse-momentum relationship)

increased time decreases the affect of applied force decreased time increases affect of applied force

How do factors like rule changes or technique adjustments influence performance and injury risk? (use impulse-momentum relationship)

technique adjustments change force and the time of force application

rule changes can change the magnitude of the force and the length of time that the impact occurs

The three basic quantities and their SI units

Mass (kg)

Length (m)

Time (s)

What is the difference between linear kinematic and linear kinetic variables?

linear kinetic variables: why of motion (with forces)

linear kinematic variables: describes motion (without forces)

Biomechanics

-the application of mechanical principles in the study of living organisms

-examining the forces acting on and within a body and the effects of these forces

Mechanics

branch of physics that analyzes the action of forces and particles of mechanical systems

Rigid Body Mechanics

application of mechanical principles to a rigid body system or rigid bodies

Rigid Body

a system of particles (a body) which does NOT deform

Statics

study of rigid bodies or systems that are in a state of constant motion (at rest or moving at a constant speed)

Dynamics

study of rigid bodies or systems that are subject to acceleration