Newtons Laws

What is newtons first law

An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force. This law is often called "the law of inertia".

What is Newtons 2nd law

Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).

Whats newtons 3rd law

For every action there is an equal and opposite reaction.

What are levers

Levers consists of two forces, an effort force and a resistance forrce acting around a pivot or fulcrum

Equilibrium: Force arm x force = resistance arm x resistance

Mechanical advantage: Force arm/resistance arm

What are first class levers?

• fulcrum located between the effort and resistance

• they change the direction of of force

• like a see saw

What is an anatomical example of a first class lever

• splenius muscle acts to extend the head across the atlanto occipital joint

• splenius muscle and teh muscles on the back of the neck act to balance the head across the atlanto occipital joint

What are second class levers?

• resistance located between the effort force and the fulcrum.

• like an wheelbarrow - mechanical advantage is always greater than 1

• in thsi arrangement, the effort must always move a greater distance than the resistance, that's to say the range of motion is always sacrificed to gain force

What is an anatomical example of a second class lever?

• These lever is rare in the body

• plantar flexion of the foot at the ankle joint

• here the pivot is the metatarso plangeal joint

• the resistance is the line of gravity while the force is the pull of the triceps surae muscle on the calcaneus bone

• again range of motion is sacrificed for the force

what is a third class lever?

• effort is located between fulcrum and resistace

• like a hammer pulling out a nail

• the effort Arm is always less than the resistance arm

• effort must be greater in magnitudee than resistance but the effort moves less distance than the resistance

• hence, there is a loss of effort but a gain in distance

What is an anatomical example of a third class lever?

• most common in the body

• permits muscles tor produce distance of movement with minimal muscles shortening although at the sacrifice of force

• biceps and many others as the insertions are so frequently found close to the joints, they move, therefore the effort is located between the pivot and resistance