Transcript Forces, Motion, and Gravity

Section 3.1
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1.
How do you think force and motion are
related?
2.
Why is gravity called a force?
3.
When you throw a ball, what happens to it
and why?
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Explain the difference in the amount of
strength you use to lift a bag of groceries, to
hold an apple, and to push a heavy box of
books.
Which takes more strength?
What causes you to need more effort?
How do you know your are using more
strength?
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Force- any push or pull
An applied force can start, stop or change the
direction of an object.
To determine the amount of force applied on
an object you need to know the mass and
acceleration of the object.
Forces are all around you. Gravity pulls you
down, muscles keep you up.
Lots of forces act on objects all the time.
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Amount and direction of most forces can be
measured.
Spring scales help measure forces.
Newton (N)- SI unit for force
 One Newton is the amount of force needed to
cause a 1-kg mass to accelerate at a rate of 1m/s2.
 1N= 1kg x 1m/sec2
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Weight of an object depends on the force
that pulls the object toward the Earth.
Acceleration due to gravity is 9.8 m/s2.
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You can determine the mass of an object by
dividing its weight by 9.8 m/s2.
What is the mass of your book if its weight is
15 N.
What about your mass?
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Look at Figure 3.2 on page 56:
 How do objects with different amount of mass
affect the spring of a spring scale?
 What causes the weight of an object?
 With what units is weight measured on the spring
scale?
 What does the spring scale show about the force
of gravity?
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When dropping objects, if no other force except
gravity acts on them, should they fall at the same
time?
 If there are other forces acting on them what’s an
example?
 Friction- the force of resistance that occurs when
movement takes place between any two objects or
substances that make contact.
 Terminal Velocity- the maximum velocity of a falling
object, occurring when the force of friction (upward)
equals the force of gravity (downward).
 All objects reach terminal velocity if given enough
time.
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Projectile motion- a curved path an object
follows if thrown horizontally.
Usually a combination of the downward
motion produced by gravity, and the
horizontal motion of the thrower.
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Give two examples of a force.
Describe how you can use a spring scale to
measure the force of gravity on an object.
3. How does friction affect a flat sheet of paper
falling through air? How would friction affect a
crumpled ball of paper? Make a generalization
about friction and falling objects.
4. If you were to throw a ball harder the second
time than the first, how would the projectile
motion change?
1.
2.
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