Ch. 4 Newton’s First Law of Motion. Motion When an object begins moving or stops moving, naturally...
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Transcript of Ch. 4 Newton’s First Law of Motion. Motion When an object begins moving or stops moving, naturally...
![Page 1: Ch. 4 Newton’s First Law of Motion. Motion When an object begins moving or stops moving, naturally we look for a cause. What might be that cause???](https://reader036.fdocuments.us/reader036/viewer/2022062408/56649f2a5503460f94c44297/html5/thumbnails/1.jpg)
Ch. 4 Newton’s First Law of
Ch. 4 Newton’s First Law of
MotionMotion
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Motion
• When an object begins moving or stops moving, naturally we look for a cause .
• What might be that cause???
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Motion
• When an object begins moving or stops moving, naturally we look for a cause .
• That cause is a push or a pull.
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Force (F)
• Any push or pull• Measured in Newtons (N)
• 1 Newton = 1 kg·m s2
Example wording: Mrs. Williams pushed the cart with a force of 5 newtons.
F = 5 N
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Force is a vector quantity.
• What does this mean?
• It has magnitude (quantity) and direction
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• Friction: a force that acts between materials as they move past each other.
• With out friction, velocity would be constant in the horizontal direction.
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Newton’s 1st Law
Law of InertiaLaw of InertiaAn object at rest will remain at rest,
and an object in motion will remain in motion, unlessacted on by an outside force.
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• Moving objects continue to move with constant velocity in the absence of a stopping force!!!!
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Journal Review Question: What might cause an object to
stop its motion? What forces are acting against it?
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• Consider a small lightweight car and a heavy truck travelling at 100 mph.
Think……. Think……. Journal: Which car will require more force to
stop its motion?
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• Think about a soccer ball at rest and a bowling ball at rest…..
Give both a sharp kick.What will be your result????
The soccer ball will have greater acceleration than the bowling ball.
The two results differ because the masses differ!
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Mass – A measure of Inertia
• Mass: the quantity of matter in an object. – measured in grams (g)
• ↑ mass an object has, ↑ Inertia
• mass inertia
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Weight: measure of force of gravity on an object.
Weight = mass x gravity w = m·g
Gravity: 9.8 m/s2 = 9.8 N/kg
1 kg = 9.8 N
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Problem Solving
• If an object has a mass of 40 kg, calculate the weight in newtons.
• w = m · g• w = 40 kg · 9.8 N
kg
w = 392 N
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Net Force• The combination of ALL forces acting on
an object.
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Net Force can be symbolized as the summation of all Forces acting on an object.
Summation symbol : ∑
∑ F = F1 + F2 + F3 + ……
Similar to the resultant. It is the result of all of the forces acting on an object!
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• Forces in the same direction are added
• Forces in opposite direction are subtracted
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• Forces at angles to each other can be resolved
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• Forces at angles to each other can be resolved
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Practice: What is the net force on each box???
A
DC
B
5 N
5 N
2 N 3 N
5 N
8 N
9 N 5 N
3 N
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Practice: What is the net force on each box???
A
DC
B
5 N5 N
2 N 3 N
5 N
8 N
9 N 5 N
3 N
7 N
2 N
9.43 N
5 N
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Equilibrium
• When net force equals zero. • Example: you standing around during lunch
– All forces acting on you are in equilibrium!!!
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• Support force, also called normal force (Fn). – Perpendicular to surface of contact
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Vectors not in the same plane…• Will balance to create a 10 N normal force• The closer the vectors are to being horizontal,
the more force is required at the point of tension to add up to the weight.
• This is why you may be able to swing from a rope that is vertical, but in the horizontal position it may snap.
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In class Ch. 4 Concept Development Practice