linear kinetics

Question 1

what is inertia?

Answer 1

•Inertia:

▫A resistance to change in motion (whether stationary or moving)

Question 2

what is mass?

Answer 2

•Mass:
▫The quantity of matter of which a body is composed
▫A direct measure of inertia

Question 3

which is easier to alter in motion, high or low mass?

Answer 3

It is easier to alter the motion of an object with less mass than it is of an object with more mass

Question 4

what is force?

Answer 4

•Force:
▫The pushing or pulling effect that one body has on another…
▫…to alter, or tend to alter, a body’s state of motion(You can apply a force but not produce motion)

Question 5

what will happen to a body in motion?

Answer 5

▫A body at rest can be made to move if sufficient force acts on it
▫A body in motion will be slowed down, sped up, or have its direction of motion changed if another body exerts force on it

Question 6

what are internal forces?

Answer 6

•Internal:
▫Any forces within the human body
Typically muscles/tendons and ligaments pulling on bones

Question 7

what are external forces?

Answer 7

•External:
▫Any forces outside of the human bodye.g. gravity, air resistance, ground reaction forces, contact forces
•We often draw free body diagrams to help understand these (external) forces

Question 8

what is a free body diagram and what is its use?

Answer 8

•A free body diagram:
▫Converts a person or object into a simple model
▫Considers the external forces acting on that person or object

•Free-body diagrams allow us to quantify the mechanics of the system more easily

Question 9

summary of forces?

Answer 9

•Weight:
force is always acting▫(Mass ×gravity)

•GRF:
is acting if there is contact with the ground▫(A reaction force will exist if there is contact with any external object)

•Drag:
force due to air resistance if the person is moving (horizontally)

Question 10

what is Newton’s First Law of motion?

Answer 10

1.Every body continues in the same state (i.e. at rest or moving at a constant velocity in a straight line) unless acted upon by an external force

Question 11

what is Newton’s Second Law of motion?

Answer 11

2.A force acting on a body causes an acceleration which is in the direction of the force and which has a magnitude inversely proportional to the mass of the body

▫Force = mass ×acceleration
▫F = ma

▫A greater force applied = greater acceleration
▫A greater mass = smaller acceleration

Question 12

Newtons second law explained

Answer 12

A force acting on a body causes an acceleration which is in the direction of the force and which has a magnitude inversely proportional to the mass of the body

▫We often have more than one force acting on a body…
▫…the object moves in the direction of, and with acceleration of proportional magnitude to, the resultant force

Question 13

what is Newton’s Third Law of motion?

Answer 13

For every force that is exerted by one body on another, there is an equal and opposite force exerted by the second body on the first

Question 14

linking the second and third laws?

Answer 14

For every force that is exerted by one body on another, there is an equal and opposite force exerted by the second body on the first

The effects that the two bodies produce on each other can be quite different

F = ma

The basketball has a mass of 0.625 kg

The Earth has a mass of ~5,972,000,000,000,000,000,000,000 kg

The acceleration caused by the equal and opposite forces will be very different between the two bodies!