Week 7 and week and 8 PDF

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Week 7 and 8 lecture notes. Linear Kinetics and Equilibrium...

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Week 7 – Linear Kinetics

7.1 Linear kinetics: Study of internal or external forces Law of Inertia: A body will maintain a state of rest or constant velocity unless acted upon by an external force that changes that state. Law of acceleration: A force applied to a body causes it to accelerate producing a magnitude proportional to the force in the direction of the force and inversely proportional to the body’s mass. F=mc2 Law of reaction: For every action, there is an equal and opposite reaction Law of gravitation: All bodies are attracted to one another with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. -9.81 m/s 2

7.2

Force of friction: Friction is a force that acts at the interface of 2 surfaces in contact in the direction opposite the direction of motion or impending motion.

The second box moved because it went past the critical point where magnitude maximum static friction has been achieved. Therefore, motion will occur, this force is now known is kinetic friction. Kinetic friction (force after magnitude maximum is achieved) < Static friction (original force before motion) Kinetic friction force remains the same regardless of the applied force = index of the interaction between 2 surfaces in contact = weight of the sled and any vertical force being applied

Pulling is easier as it decreases the magnitude of the reaction force by reducing the downward vertical weight force which then reduces the reaction force, and therefore reduced the friction force. Pushing is opposite Linear momentum (vector quantity): quantity of motion calculated as the product of the body’s mass and its velocity

Player 2 has greater momentum so that’s collision.

the direction they will go after the

Impulse: A force that starts a body into motion, the motion produced by a starting force, a strong sudden desire to do something She resisted the impulse to shout. Impulse = force x time Impact collision: exchange of a large force during a small-time interval

When 2 bodies undergo a direct collision, the difference in their velocity immediately after impact is proportional to the difference in their velocities immediately before the impact.

7.3 Work: force applied against a resistance x displacement of the resistance in the direction of the force Work = Neuton Meter When both the net muscle moment and the direction of angular motion at the elbow are in the same (opposite for negative) direction the work done positive. Alternatively, its negative Power:

Energy: capacity to do work. Two forms of energy (potentional and kinetic) Potential energy: energy of the position Kinetic energy: energy of motion

If the body isn’t moving. Its kinetic energy is 0 Law of conservation of mechanical energy. As the ball gets higher, the Potential energy gets bigger and the kinetic energy gets smaller. Once it reaches it apex, there is maximal Potential energy and 0 kinetic energy. When gravity is the only external force, a body’s mechanical energy remains’ constant. The work of a force is equal to the change in energy that it produces in an object acted on

Work = change in Kinetic energy + change in Potential energy + change in Thermal energy (heat)

Week 8 – Equilibrium

8.2 Moment (rotary force): Angular force is the product of the applied force and the force’s moment arm. Or the perpendicular distance from the force’s line of action to the axis of rotation. A moment is influenced by the magnitude of the force and the length of its moment arm. The moment arm for a muscle with respect to a joint centre is the perpendicular distance between the muscle’s line of action and the joint centre.

When the bicep pulls on the forearm and he angle reaches 90 degrees, the moment arm is at its largest. This is the perpendicular distance from the intersection to the axis of rotation. As the forearm moves away from the 90 degrees in either direction, the moment arm for the biceps brachii progressively changes. A muscle to generate a constant joint moment during an exercise, it must produce more force as its moment arm decreases. The triceps group controls the velocity of the moment and enhances the stability of the elbow joint as the agonist bicep group develops tension. When the net moment and joint motion occur in the same direction the moment is termed concentric and the muscle moment in the opposite direction is called eccentric. Directly measuring force produced by muscles is not possible to estimates of resultant joint moments are often used to investigate the pattern of muscle use. Influenced by the weight of the body’s segment, the motion of the body’s segment and the action of external forces. Additionally, movement speed will influence joint motion. When speed of movement is increases, you’ll that the resulting moment during exercises will increase....