Chapter 3: Mechanics PDF

MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES Chapter 3: Mechanics Dr. Ohoud Aljawi MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES Learning Outcomes: 1.Identify Mechanics, Biomechanics, Kinematics, Dynamics and statics. 2.Differentiate between distance and displacement 3.Differentiate between sp...

MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES Chapter 3: Mechanics Dr. Ohoud Aljawi MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES Learning Outcomes: 1.Identify Mechanics, Biomechanics, Kinematics, Dynamics and statics. 2.Differentiate between distance and displacement 3.Differentiate between speed and velocity. 4.Apply equations of motion to solve problems. MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES Mechanics Is the branch of physics dealing with the effect of forces on the motion of bodies. T O D AY ' S Q U O T E • Biomechanics Is concerned with movement and physical behavior of muscles, bones and organs such as the lungs and the heart. • • The development of artificial limbs and mechanical hearts is an active area of biomechanical research. 2.1 Mechanics MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES Kinematics: It is the part of mechanics concerned with description of motion; how much (time), how far (distance and displacement), how fast (speed and velocity) and change in velocity (acceleration). • Dynamics: Concerned with causes of motion. • Statics: Deals with non-moving objects in equilibrium – example: levers as will be explained later. T O D AY ' S Q U O T E • 1. Distance and Displacement MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES Is the length of path the object takes in moving from one place to another. Distance is a scalar quantity that does not depend on direction. d = distance, The SI unit is meter (m). T O D AY ' S Q U O T E • Distance: • Displacement: Is the change in position of the object, and has a direction from initial to final position. • It is a vector quantity. • ՜ or d= displacement, The SI unit is meter (m) 𝑑 MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES Exercise: Different distance and displacement T O D AY ' S Q U O T E A boy walks 4 meters East, 2 meters South, 4 meters West, and finally 2 meters North. Determined the distance and the displacement? 4m Total distance = 12 m Total displacement = 0 2m 2m 4m T O D AY ' S Q U O T E MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES T O D AY ' S Q U O T E MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES T O D AY ' S Q U O T E MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES T O D AY ' S Q U O T E MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES 2. Speed and Velocity • MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES Speed and velocity are similar; but they are different physical quantities: • Speed: T O D AY ' S Q U O T E Is a scalar quantity. It is the distance traveled divided by the time taken. ∆𝑥 𝑑 𝑣 = or 𝑣 = ∆𝑡 ∆𝑡 • Velocity: is • a vector quantity. It is the displacement (change in position) divided by the time taken. ՜= 𝑣 ∆𝑥 ՜ 𝑑 or 𝑣= ∆𝑡 ∆𝑡 The SI unit for both is (m/s). 2. Speed and Velocity If the body is moving in a circle, the speed may be constant but the velocity is changing, because the direction is changing. T O D AY ' S Q U O T E • MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES 3. Acceleration MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES When the velocity of an object changes with time, the body has acceleration. • The acceleration can be due to change in speed, change in direction of motion or both of these. • Acceleration is a vector quantity since velocity is a vector. • When the acceleration is opposite to velocity, the velocity of the body decreases. • A body may have acceleration when moving with constant speed, this happens in circular motion. Here the acceleration vector is perpendicular (at 90 degrees) to the velocity vector. T O D AY ' S Q U O T E • 3. Acceleration MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES We consider only objects moving in a straight line in one direction. And the velocity of an object increases, we say it accelerates; when it decreases, we say it decelerates. The SI unit for the acceleration is (m/s2). ∆𝑣 ՜= 𝑎 ∆𝑡 T O D AY ' S Q U O T E • 3. Acceleration INSERT PICTURE HERE If ՜ points in the same direction as ՜ , the body is accelerating. • • MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES 𝑎 𝑣 If ՜ points to the opposite direction of ՜ , the body is decelerating. 𝑎 𝑣 INSERT PICTURE HERE INSERT PICTURE HERE MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES INSERT PICTURE HERE A motor scooter undergoes acceleration when it A. INSERT speeds PICTURE up. HERE B. slows down. C. changes direction. D.All of these. INSERT PICTURE HERE MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES INSERT PICTURE HERE A motor scooter undergoes acceleration when it A. INSERT speeds PICTURE up. HERE B. slows down. C. changes direction. D.All of these. INSERT PICTURE HERE MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES Acceleration due to Gravity INSERT PICTURE HERE • Galileo found that objects falling freely downwards towards the earth has the same called acceleration due to gravity. INSERT acceleration PICTURE INSERT PICTURE HERE HERE • Acceleration due to gravity always points downwards. • Thus, objects thrown upwards experience deceleration (՜ and ՜ are in 𝑎 opposite directions). 𝑣 MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES 4. Equations of Motion • If INSERT PICTURE HERE a body starts motion at a velocity ՜ (initial, or starting velocity), and 𝑣𝑖 reaches a velocity 𝑣𝑓 INSERT PICTURE (final velocity) in a time then: INSERT PICTURE HERE HERE • Eq. (1) 4. Equations of Motion • Average velocity: MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES INSERT PICTURE HERE Sometimes we don’t need the instantaneous velocity; we just need to calculate the total distance covered in some time. Here we talk about PICTURE INSERT PICTURE the averageINSERT velocity. HERE HERE Eq. (2) • Also when the acceleration is constant, Eq. (3) 4. Equations of Motion • From MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES INSERT PICTURE HERE the above equations, we can write INSERT PICTURE HERE INSERT PICTURE HERE Eq. (4) Eq. (5) Example MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES INSERT PICTURE HERE 2 m/s An airplane acceleration down a runway at 3.20 for 32.8 s unit is finally lifts off the ground. Determine the distance traveled before takeoff INSERT PICTURE INSERT PICTURE HERE HERE Example MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES INSERT PICTURE HERE A car starts from rest and accelerates uniformly over a time of 5.21 seconds for a distance of 110 m. Determine the acceleration of the car INSERT PICTURE INSERT PICTURE HERE HERE Example MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES INSERT PICTURE HERE A race car accelerates uniformly from 17 m/s to 45.1 m/s in 3 seconds. Determine the acceleration of the car and the distance travelled?INSERT PICTURE INSERT PICTURE HERE HERE MOHAMMED AL-MANA COLLEGE FOR MEDICAL SCIENCES THANK YOU