Biomechanics Final

Momentum

A product of mass and velocity that represents the quantity of motion. Indicated how difficult it is it speed up or slow down an object

Two simple collision scenarios

1. Collision between two objects of equal mass with one object stationary pre-collision (Cue ball in pool)

2. Collision where objects have same post-collision velocity (Head on collisions by moving the same direction after the collision)

Coefficient of restitution

Ratio of velocities describing bounciness via a conversion of kinetic energy (How much energy is lost)

• e = sqrt of (bounce height / drop height)

Perfectly elastic

e =1, there is no kinetic energy lost. Ex cue ball

Perfectly inelastic

e=0, Maximum loss of kinetic energy

Not perfectly elastic

0<e<1, most collisions

Two ways to check answers for momentum

1. Calculate the post collision momentum of the system (This should be equal to the pre collision) → This method shows understanding of conservation of movement

2. Calculate one post collision velocity using the original momentum formula

Force

a push or pull that may accelerate or deform an object

Force measurement

Newtons

Internal acting force

Acts within a system but do not influance the motion of the object of the system

External acting force

Act on object due to an interaction with environment or other objects and these forces may accelerate objects

4 direction of force

1. Compression

2. Tension

3. Bending

4. Torsion

Two ways that forces act

1. Contact - force occur due to touching objects

2. Non contact - forced present without touching or contacting an object

Mass

Proportional to the amount of matter in object and reflects an object inertia

Weight

the force acting on a object due to gravitational acceleration

Gravity

Attraction between all objects with mass

Newtons first law

An object at rest will stay at rest unless acted on by a force

What does a graph look like when trying to push

The graph will increase at 45 degrees and then drop and plateau

Is it harder to start and object or keep it sliding?

Harder to start because the force acting on the object must exceed the force of friction.

Dry friction

No lubrication between bodies

Fluid friction

There is fluid or lubrication on the surface which changes the surface properties

Static friction

Occurs between two objects that are NOT sliding

Dynamic/Kinetic friction

Occurs between two objects that are sliding

What does friction force depend on

Surface properties and the normal force

Normal force

Force acting perpendicular to the surface

u=1

means it takes as much force to pull and object then lift it

u<1

Normal coefficient of friction

is it safer to pull or lift an object and why?

Safer to pull an object because the coefficient of friction are less then 1