1. Related to Chapters 3 and 1 in the text
Newton & Biomechanics
Related to Chapters 3 and 1 in the text
5/7/2019
Dr. Sasho MacKenzie - HK 376

2. Where does the bottle go?
A disorderly HK student leaves the Inn and is walking towards The Pub holding a bottle. In an attempt to heckle a stop sign for looking stupid, the bottle slips from his hand. What path would it follow to its tragic end?
Direction of stumble C A B
5/7/2019
Dr. Sasho MacKenzie - HK 376

3. Newton’s First Law of Motion
An object continues to stay at rest or move in a straight line until an external force acts on it.
After release, the bottle continues to move with the same horizontal velocity as the student, but without the force of the hand balancing out the force of gravity, it also accelerates vertically to the ground.
Thus following a curved path with independent horizontal and vertical velocities.
5/7/2019
Dr. Sasho MacKenzie - HK 376

4. When does the ball have the greatest speed?
During a golf drive, does a golf ball have the most speed
Halfway between when it was struck and its peak height.
About 10 to 20 meters after it has been struck.
The instant it loses contact with the clubface
5/7/2019
Dr. Sasho MacKenzie - HK 376

5. Newton’s Second Law of Motion
The acceleration of an object is proportional to the net force acting on it. The acceleration is also in the same direction as the force.
F = ma
The golf ball will accelerate and thus gain speed until the instant it leaves the clubface. Air resistance then becomes the dominant force, and the ball accelerates negatively.
5/7/2019
Dr. Sasho MacKenzie - HK 376

6. Carl (170 lbs) vs. The Bus (50,000 Lbs)
Carl decides to take his chances by crossing the street in front of a bus. Carl eats pavement because
The bus hit Carl with more force
Carl didn’t want it bad enough
Carl succumbed to a greater acceleration because of his reduced mass (inertia)
5/7/2019
Dr. Sasho MacKenzie - HK 376

7. Newton’s Third Law of Motion
For every force, there is an equal and opposite force.
Carl and The Bus impart equal but opposite forces on each other.
Carl eats pavement because he undergoes a greater acceleration due to his smaller inertia.
a = F m
5/7/2019
Dr. Sasho MacKenzie - HK 376

8. Clean and Jerk…example question
What force is required to lift a 100 kg weight off of the ground with an acceleration of 5 m/s/s?
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Dr. Sasho MacKenzie - HK 376

9. Newton’s Law of Universal Gravitation
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Dr. Sasho MacKenzie - HK 376

10. What is gravity It is a force
The force of attraction between two objects
The force of gravity produces an acceleration of about 9.81 m/s/s on all objects in free fall “near” the earth’s surface (if air resistance was neglected).
This force is directed towards the center of the earth and therefore so is the acceleration
5/7/2019
Dr. Sasho MacKenzie - HK 376

11. Newton’s Law of Universal Gravitation
All objects attract each other with a force that is inversely proportional to the square of the distance between them.
This force is proportional to the mass of the two bodies under consideration.
Have not been proven. But they do stand up test after test via inspection
F is the force of gravity, G is the gravitational constant, m1 and m2 are object masses, and r is the distance between the centers of mass of the objects.
F = G m1m2 r2
5/7/2019
Dr. Sasho MacKenzie - HK 376

12. Gravitational Force = Weight
The earth’s gravitational force acting on an object, is the object’s weight.
For an object close to the earth’s surface, the variables G, m2, and r become constant so we can replace them in the equation with, g, which is equal to 9.81 m/s/s.
F = G m1m2 r2 1.
g = G m = 9.81 m/s/s r2 3.
F = m1 * G m2 r2 2. 4.
F = m1g = mg = W
5/7/2019
Dr. Sasho MacKenzie - HK 376

13. Earth Parameters Mass = 5.9763 x 1024 kg =
Radius at Equator = km
Average Radius = km
Radius at Pole = km
Angular Velocity = 360/24 hrs = /s = rad/s
Ask them to calculate the velocity of the classroom relative to a stationary point in space?
5/7/2019
Dr. Sasho MacKenzie - HK 376

14. Gravity related question
Relative to a stationary point in space what is our linear velocity due to the earth’s rotation if we are sitting at the equator?
What about at the North Pole?
Where is the traveler?
5/7/2019
Dr. Sasho MacKenzie - HK 376

15. Bob Beamon at the Mexico City Olympics in 1968
Beamon's world record (8.90 m; 29 ft. 2½ in.) stood for 23 years, and was named by Sports Illustrated magazine as one of the five greatest sports moments of the 20th century. Beamon’s world record was finally broken in 1991 when Mike Powell jumped 8.95 m (29 ft. 4-3/8 in.) at the World Championships in Tokyo, but Beamon's jump is still the Olympic record and 40 years later remains the second longest of all time.
Bob Beamon at the Mexico City Olympics in 1968
At an altitude of 2240 m (7349 ft), Mexico City's air had less resistance than air would have at sea level. What about gravity?
5/7/2019
Dr. Sasho MacKenzie - HK 376

16. Bob Beamon at the Mexico City Olympics
5/7/2019
Dr. Sasho MacKenzie - HK 376