Download 1 - Eickman

Ch. 15: Forces and Motion
Lesson 4: What are the laws of motion?
1. Name 2 scientists
who studied motion.
Galileo, Newton
2. State Newton’s 1st
Law of Motion.
An object at rest remains at rest, and an object in
motion remains in motion at constant speed and in
a straight line, unless acted on by an unbalanced
force
3. What happens to
an object at rest if
two balanced forces
act on it?
It stays at rest
4. Why does a kicked
soccer ball eventually
quit moving?
Friction is the unbalanced force that makes it slow
down and stop
5. Define inertia.
Tendency of an object to remain at rest or in
constant motion unless a force acts on it
6. Which has greater
inertia, a beach ball
or a bowling ball?
Explain.
Bowling ball – more mass causes more inertia
7. It takes 3 people
to get a heavy object
to start moving, but
once it’s moving it
only takes 2 people to
keep it moving. Why?
Static friction is greater than rolling or sliding
friction – also the object wants to keep moving
because of inertia
Ch. 15: Forces and Motion
Lesson 4: What are the laws of motion?
8. An object moves
in circular path at a
constant speed. Are
the forces on the
object balanced?
Explain.
No – if the forces were balanced it would move in
a straight line – unbalanced forces cause objects
to change speed or direction
9. State Newton’s 2nd
Law.
The acceleration of an object depends on the mass
of the object and the size of the net force applied
10. The same
unbalanced force is
applied to objects A,
B, and C. Object B
has the greatest
acceleration, and
object A the least.
Rank the masses of
the three objects.
B has the smallest mass because it has the biggest
acceleration (smaller mass is easier to accelerate)
C has the middle mass
A has the largest mass because it has the least
acceleration (larger mass is harder to accelerate)
11. Suppose you are
riding on a bicycle.
You stop to place a
heavy object on the
back of the bike.
How will the
increased mass affect
the bike’s
acceleration if you
pedal with the same
force? Explain.
If you pedal with the same force, the acceleration
will be less. Larger mass is harder to accelerate.
12. Write the
equation for
Newton’s 2nd Law.
Acceleration = force/mass
Ch. 15: Forces and Motion
Lesson 4: What are the laws of motion?
13. An object has a
mass of 12 kg. A
force of 36 N is
applied to it. What is
the objects
acceleration?
36/12 = 3 m/s2
14. A ball with a
mass of .2 kg is
kicked with a force of
5 N. What is the balls
acceleration?
5/.2 = 25 m/s2
15. State Newton’s
3rd Law.
When a force is applied to an object, the object
exerts an equal force in the opposite direction
16. Why does a
rubber ball bounce?
Ball exerts force on ground and ground exerts and
equal and opposite force on the ball which makes
it move up
17. For every ______
there is an equal and
opposite ______.
Action; reaction
18. Give some
examples of the
statement in #17.
Feet push on ground and ground pushes on feet
while walking; you pull on doorknob while
doorknob pulls on you
19. You apply a force
to a soccer ball when
you kick it. Compare
this force to the force
that the soccer ball
exerts on your foot.
They are equal in strength and opposite in
direction
Ch. 15: Forces and Motion
Lesson 4: What are the laws of motion?
20. A ball rolls down
a lane and strikes a
pin. Which is
greater, the force of
the ball on the pin or
the force of the pin
on the ball? Explain.
They are equal. Every action has an equal and
opposite reaction
21. Define
momentum.
Force needed to stop a moving object
22. Which has
greater momentum, a
car sitting still or a
pebble rolling down a
hill? Explain.
Pebble rolling. Car isn’t moving.
23. State the law of
conservation of
momentum.
Total momentum before a collision equals total
momentum after the collision
24. In a game of
pool, the six-ball
collides with the tenball, which was
originally at rest.
The collision causes
the six-ball to stop.
Predict the motion of
the ten-ball after the
collision, assuming
both balls have the
same mass.
Ten-ball should move at the same velocity as the
six-ball was originally.
25. An adult and a
child are ice skating.
The child pushes
away from the adult.
The child moves
backward. What will
happen to the adult?
Adult will move in the opposite direction but at a
slower velocity because the adult has larger mass.