Ch.3 Linear Kinetics

What is kinetics?

- A study of force and its effects on the object’s motion

What is linear kinetics?

- study of force and its effects on the object’s linear motion

What is inertia?

- property of an object to resist changes in its motion
- determined by object’s mass

What is linear momentum (L)?

- product of mass and velocity of COM that represents the “quantity of motion”

What determines linear momentum?

- object’s mass
- linear velocity

What is linear impulse (J)?

- sum of forces applied to the object over a period of time

What determines linear impulse?

- average net force applied to object
- duration of force application

What is linear acceleration (a)?

- rate of change in magnitude and/or direction of linear velocity

What is Newtons 1st Law?

- object at rest will remain at rest, and object in motion will remain in motion when the net force acting on it is 0

What is the law of conservation of linear momentum?

- when the net force acting on the object is 0, linear momentum of object remains constant

What changes object’s momentum?

- object’s momentum is changed by the impulse produced on the object

What can be analyzed using law of conservation of linear momentum?

- velocity and momentum of objects in collision

Is there an impulse produced during a collision?

- yes, but considered negligible because duration of force application is very small

What happens to the momentum during collisions?

- momentum of the group stays the same but momentum can be transferred between the objects depending how the objects move after the collision

How does momentum transfer when objects start to move as a single object (move same way)?

- no momentum was transferred between

What determines how much momentum gets transferred between object during collision?

- coefficient of restitution (index of bounciness/elasticity between objects)

What are the coefficient of restitution (e) characteristics?

- ranges 0-1
- higher coefficient of restitution between objects, more momentum gets transferred between objects

What is the law of acceleration?

- when net force is acting on an object, object will accelerate in direction of net force
- acceleration is proportional to net force and inversely proportional to mass

How does the law of acceleration relate to a barbell bench press exercise?

- positive net force acting on barbell moving upward will speed up upward movement
- positive net force on barbell moving downward will slow down downward movement

What factors affect acceleration?

- greater net force applied, greater acceleration
- greater mass of object, smaller acceleration

What relationship does the law of acceleration describe?

- between impulse and change in object’s momentum
- instantaneous relationship between net force and acceleration

What is impulse-momentum relationship?

- impulse applied to object (causes) equals the change in object’s momentum

What can impulse do to momentum?

- generate (impulse and object motion in same direction, increases momentum)
- absorb (impulse and object motion in opposite direction, decreases momentum)

What does impulse-momentum relationship allow us to understand?

- effects of duration of force application on the force required to change object’s momentum

What is the law of reaction?

- for every action there is always an opposite and equal paired reaction force

What are characteristics of paired forces?

- equal in magnitude and opposite in direction
- act on different objects

Are the effects of paired forces equal?

- no, they are not always equal

Will the paired forces act on different objects with the same mass?

- no, the mass may differ
- small mass, greater acceleration than force acting on larger mass object