Do Now 10.21.10

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# Do Now 10.21.10 - PowerPoint PPT Presentation

(When blocking in football, why does a defending lineman often attempt to get his body under that of his opponent and push upward?) What effect does this have on the friction force between the opposing lineman’s feet and the ground?. Do Now 10.21.10.

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(When blocking in football, why does a defending lineman often attempt to get his body under that of his opponent and push upward?) What effect does this have on the friction force between the opposing lineman’s feet and the ground?

Do Now

10.21.10

What is the net force acting on a ball at each point?

(ignore air resistance)

10 m/s

C

5 m/s

10 m/s

B

5 m/s

10 m/s

10 m/s

10 m/s

A

10 m/s

10 m/s

Do Now 10/21

Chapters 2, 3, and 6

• Newton’s 1st Law (Inertia)
• Newton’s 2nd Law
• Friction
• Air Resistance
Test Tuesday

Explain freefall forces

• State the two factors that affect air resistance
Objective

6.6Free Fall Explained

The ratio of weight (F) to mass (m) is the same for the 10-kg cannonball and the 1-kg stone.

6.7Falling and Air Resistance

The air resistance force an object experiences depends on the object’s speed and surface area.

6.7Falling and Air Resistance

Terminal Speed

Terminal speed isthe speed at which the acceleration of a falling object is zero because friction balances the weight.

6.7Falling and Air Resistance

Sky divers reach terminal speed when air resistance equals weight.

6.7Falling and Air Resistance

• The terminal speed for a sky diver varies from about 150 to 200 km/h, depending on the weight and orientation of the body.
• A heavier person will attain a greater terminal speed than a lighter person.
• The heavier person’s weight “pushes” through the air particles with greater force
• Body orientation also makes a difference. Dive vs. Spread out.

6.7Falling and Air Resistance

The flying squirrel increases its area by spreading out. This increases air resistance and decreases the speed of its fall.

6.7Falling and Air Resistance

A parachute will bring the skydiver’s speed to about 15 km/h to 25 km/h

6.7Falling and Air Resistance

think!

Which experiences a greater air resistance force, a falling piece of paper or a falling elephant?

6.7Falling and Air Resistance

think!

Which experiences a greater air resistance force, a falling piece of paper or a falling elephant?

Answer:The elephant! It has a greater frontal area and falls faster than a piece of paper—both of which mean the elephant pushes more air molecules out of the way. The effect of the air resistance force on each, however, is another story!

A falling 50-kg parachutist experiences an upward acceleration of 6.2 m/s2 when she opens her parachute. What is the force of friction acting on her?

Practice

4 m/s2 and 2 m/s2

• 3 kg
• 6 m/s2
• 1 m/s2
• 3 m/s2
• 12 m/s2
• Half as fast
• 140,000 N
• 15 m/s2
• 7.5 m/s2

a = 0.25 m/s2

• Fnet = 0 N
• a = 0 m/s2
• a = 2 m/s2
• a = 1 m/s2
• a = 10 m/s2
• FN = 80 N, m = 8 kg, a = 5 m/s2, Fnet = 40 N
• FN = 100 N, μ = 0.1, m = 10 kg, a = 1 m/s2, Fnet = 10 N
• FN = 50 N, Ff = 5 N, Fg = 50 N, a = 1 m/s2, Fnet = 5 N
• μ = 0.167
• Fa = 105 N, Fa = 0 N