Linear Kinetics Flashcards

Linear Kinetics

A study of force and its effects on the object's linear motion.

Inertia

The property of an object to resist changes in its motion.

Determined solely by mass (kg).

Unit: kg

Inertia: The greater the _____, the greater the inertia and the greater the resistance to acceleration.

mass

Linear Momentum (L)

Represents the "Quantity of motion". It is the product of the mass and the velocity of the center of mass.

Formula: L = mv.

Unit: kg·m/s

Linear Impulse (J)

Sum of the forces (ΣF) applied to the object over a period of time (Δt).

Formula: J = ΣF

Δt. Unit: Ns

Linear Impulse (J) is determined by two factors:

Average net force and the duration of force application.

Linear Acceleration (a)

The rate of change in magnitude and/or direction of the linear velocity.

Formula: a = Δv / t.

Unit: m/s²

Newton's 1st Law Condition

The net force (ΣF) acting on the object is 0.

Motion at Rest (v = 0 m/s) will...

remain at rest.

Motion in Motion will...

remain in motion.

If net force (ΣF) acting on the object is 0, an object's linear velocity and momentum is....

conserved.

Law of Conservation of Linear Momentum

When ΣF = 0, the linear momentum (L) of the object remains constant.

Momentum is changed only by impulse (ΣF Δt) produced on the object.

Momentum during Collision

Combined total momentum of colliding objects is conserved because Δt is very small, making outside impulse negligible.

Momentum can be transferred between objects.

Newton's 2nd Law Condition

The net force (ΣF) acting on the object is NOT 0.

Result of Net Force

The object will accelerate in the direction of the net force.

Proportionality of Acceleration

Acceleration (a) is proportional to net force (ΣF) and inversely proportional to mass (m).

Formula: a= ΣF/m

As the mass of an object increases, what is the impact on its acceleration if net force remains constant?

Acceleration will decrease.

Effect on Speed (Same Direction)

If ΣF and velocity (v) have the same direction, the object will speed up.

Effect on Speed (Opposite Direction)

If ΣF and velocity (v) have opposite directions, the object will slow down.

Newton's 3rd Law Principle

For every force there is always a paired reaction force.

Characteristics of Paired Forces

Equal magnitude, opposite direction, act on different objects.

Effect of Paired Forces

Acceleration depends on the mass of the object.

Smaller mass → greater acceleration.

How does increasing time of a momentum-absorption impact net force production?

It minimizes net force and therefore injury risk

Impulse-Momentum Relationship

Impulse (ΣF Δt) equals the change in momentum (m Δv).

Formula: ΣF Δt = m Δv

What causes a change in momentum?

an impulse

Generating Momentum

Occurs when impulse and motion are in the same direction.

Absorbing Momentum

Occurs when impulse and motion are in opposite directions.

Force Management

To reduce required force (ΣF), increase duration of force application (Δt).

Formula: ΣF = mΔv / Δt

Coefficient of Restitution (e)

Index of elasticity or "bounciness" between colliding bodies.

Indicates momentum transfer.

Range of e

Ranges between 0 and 1.

Perfectly Elastic Collision

e = 1. Objects bounce off with same relative velocity. 100% momentum transfer.

Perfectly Plastic Collision

e = 0. Objects stick together. 0% momentum transfer.

Relative Velocity Formula

e = |Relative velocity after impact| / |Relative velocity before impact|

Head Impact Protection (Newton's 2nd Law)

Anticipating impact allows head and trunk to move as one mass.

Larger mass → smaller acceleration (a = ΣF / m), reducing injury risk.