1. Newton’s 2nd Law
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2. Newton’s 2nd Law
Newton’s 1st law explains what causes things to move or stop moving.
Newton’s 2nd law explains the relationship between force, mass and acceleration.
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3. Newton’s 2nd Law
Newton’s 2nd law states that the acceleration of an object is in the same direction as the net force on the object. It also states that acceleration can be calculated with the following equation…
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4. Newton’s 2nd Law This is the equation for Newton’s 2nd law…
Force = Mass x Acceleration
Force (newton’s)
Mass (kilograms)
Acceleration (m/s/s or m/s2)
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5. Example
Jessica and Laura are sledding. Their combined mass is 70 kg. They are accelerating at a rate of 0.5 m/s^2. What is the net force on the sled.
M = 70 kg
A = 0.5 m/s^2
F = ma. 70 x 0.5 = 35 N
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6. Try this!
What is the net force on a car with a mass of 1000 kg if its acceleration is 35 m/s^2?
35,000 N
(this one is tricky) A car is being towed. What is the car’s mass if the net force on the car is 4,000 N and it has an acceleration of 2.5 m/s^2?
F = ma, so 4,000 = m x 2.5
M = 1,600 kg
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7. More!
The mass of a helicopter is 4,500 kg and the net force on it is 18,000 N. At what rate is the helicopter accelerating?
F = ma
F = 18,000 N, m = 4,500 kg
18,000 = 4,500 x a
A = 4 m/s^2
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8. Friction
Friction: the force that opposes the sliding motion of two surfaces that are touching each other.
The amount of friction depends on two factors:
Type of surface
Amount of force pushing the surfaces together
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9. Static Friction
Static friction: the frictional force that prevents two surfaces from sliding past each other.
The word ‘static’ means “to stay”
This is the type of friction that prevents you from moving something.
Example: You try and push a tractor trailer and it does not move. This is due to static friction.
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10. Sliding Friction This is the opposite of static friction.
This is the type of friction that occurs between two objects that are sliding past one another.
Once you stop pushing one of the objects the sliding friction is what causes the item to stop moving.
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11. Rolling Friction
Like the other types of friction, this is exactly what it sounds like.
This is the type of friction that exists between an object that is rolling and the surface it is rolling on.
Example: A car is rolling while your foot is on the gas. You take your foot off the gas and the car comes to a stop because of rolling friction.
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12. Air Resistance
Air resistance is resistance caused by the air (pretty self explanatory).
If there were NO air, two objects would fall at the same speed and same acceleration.
Example: If a bowling ball and a feather were dropped on the moon, they would hit the moon at the same time.
Because we have air all around us, different objects will pick up different amounts of air resistance and fall at different speeds.
Example: If a bowling ball and a feather were dropped on the earth, they would hit the ground at different times because of the air resistance.
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13. Air Resistance
The amount of air resistance is dependent upon the speed, size and shape of the object.
Air resistance is WHY a plastic bag would float to the ground slower than a bowling ball. It has NOTHING to do with the mass of the object!!!
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14. Terminal Velocity
Terminal velocity is the fastest speed a falling object will reach.
Objects have a terminal velocity because of air resistance.
When the force of gravity on an object and the force of air resistance are equal, the object has met it’s terminal velocity.
At terminal velocity, an object is no longer accelerating, but traveling at a constant speed (velocity).
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15. Thank You
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