Newtons Second Law of Motion Force Acceleration Newtons

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Newton’s Second Law of Motion

Newton’s Second Law of Motion

Force & Acceleration Newton’s First Law of Motion, Zero Force implies Constant Velocity (same

Force & Acceleration Newton’s First Law of Motion, Zero Force implies Constant Velocity (same as uniform motion) Definition of Acceleration, (Acceleration) = (Change in Velocity) (Time interval)

Force & Acceleration From those two results we have that, Velocity implies Object Net

Force & Acceleration From those two results we have that, Velocity implies Object Net Force implies not Accelerates not Zero Constant

Force & Acceleration Larger the net force, greater the acceleration implies Double the Force

Force & Acceleration Larger the net force, greater the acceleration implies Double the Force Triple the Force Half the Force implies Acceleration “goes as” Force “goes as” Acceleration. Double the Acceleration Triple the Acceleration Half the Acceleration Mathematically, we write Force ~ Acceleration. Think about Cars and Motors

Check Yourself You push on a crate with 100 Newtons of force. If the

Check Yourself You push on a crate with 100 Newtons of force. If the friction force is 100 Newtons, does the crate accelerate? No, because net force is zero. Does that mean that the crate is not moving? No, just that its velocity is constant.

Check Yourself (cont. ) Now push with 150 N; friction is still 100 N.

Check Yourself (cont. ) Now push with 150 N; friction is still 100 N. Does the crate accelerate? Yes, because net force is now 50 Newtons. A friend helps push with an additional 150 N. By how much does acceleration increase? Net force is now 150+150 -100= 200 N. This is FOUR times larger so acceleration increases by a factor of four.

Mass & Acceleration For a given force, greater mass, smaller the acceleration Double the

Mass & Acceleration For a given force, greater mass, smaller the acceleration Double the Mass Triple the Mass Half the Mass Acceleration goes as the inverse of mass. implies Half the Acceleration Third of the Acceleration Double the Acceleration Mathematically, we write, Acceleration ~ 1/(Mass). Think about a shopping cart

Check Yourself NO FRICTION ? ? ? ? ?

Check Yourself NO FRICTION ? ? ? ? ?

Newton’s Second Law of Motion The acceleration of an object is directly proportional to

Newton’s Second Law of Motion The acceleration of an object is directly proportional to the net Force applied to the object and inversely proportional to the mass of the object. Mathematically written (Acceleration) = (Net Force) (Mass) A=F/M also could be written as F= M x A

Bowling Ball in a Bag Carry 6 kg bowling ball in a grocery bag.

Bowling Ball in a Bag Carry 6 kg bowling ball in a grocery bag. How much weight does the bag support? Weight is (6)x(9. 8) = 58. 8 Newtons. If I quick yank upwards, accelerating by 5 m/s 2, how much additional force is required? Extra force is (6)x(5) = 30 Newtons and the total force is 88. 8 Newtons.

Weight on Earth Acceleration of gravity on Earth is 9. 8 meters per second.

Weight on Earth Acceleration of gravity on Earth is 9. 8 meters per second. (Notation: g = 9. 8 m/s 2 ) From Newton’s Second Law, (Force) = (Mass) X (Acceleration) For example, weight (force of gravity) for 1 kg is ( 9. 8 Newtons ) = ( 1 kg ) X ( 9. 8 m/s 2 )

Newton’s Second Law explains why all objects fall with same acceleration. Free Fall Acceleration

Newton’s Second Law explains why all objects fall with same acceleration. Free Fall Acceleration Ratio of weight/mass always the same since weight depends on mass.

Falling in a Vacuum Feather falls slowly due to air resistance force. If we

Falling in a Vacuum Feather falls slowly due to air resistance force. If we remove the air (create a vacuum) then feather and coin fall with same acceleration.

Air Resistance (Drag) Origin of drag is molecules of gas (or liquid) striking a

Air Resistance (Drag) Origin of drag is molecules of gas (or liquid) striking a moving object. (Friction in the air!) Drag force depends on: • Size (area) of the object • Speed of the object Larger the size or speed, larger the drag. Also depends on shape of object, density of gas or liquid, etc.

Terminal Velocity Speed of falling objects increases until drag force balances weight. When forces

Terminal Velocity Speed of falling objects increases until drag force balances weight. When forces balance, zero acceleration so constant velocity. Speed for which air resistance balances weight called terminal speed. High terminal speed (better open the chute!) Low terminal speed (large area of chute)