Transcript Motion Review

Motion
Review
 What
kinds of forces cause an object to
change its motion?
 Unbalanced forces
 What
might happen if an unbalanced
force acts on a moving car?
 It would slow down/stop/crash
 What
effect does balanced forces have
on motion?
 NO MOTION
 What
is speed?
 Distance per time
 What
is velocity?
 Speed and direction
 What
is acceleration?
 Change in velocity

Either change in speed or direction, or
both!
 What
is the law of conservation of
momentum?
 Momentum before a collision equals the
momentum after a collision
 How
does Newton’s Cradle represent
conservation of momentum?
 The same number of objects that collide
on one side move on the other
 Draw
all of the forces acting on you as
you sit still in your chair.
 Draw
the action reaction pairs for:
A larger student and smaller student sit on
skateboard. The larger student pushes on the
hands of the smaller student.
 If
a student it sitting on a skateboard with
a heavy medicine ball, then he throws the
medicine ball in front of him. Which
direction will he move?
 Backward
 Which
law explains why the student in the
previous example would move
backwards?
 Newton’s 3rd: Action-Reaction
I
have penny inside a balloon. If I get the
penny to spin around at a constant
velocity, is it accelerating? Explain.
 Yes because it is constantly changing
direction
 What
is another name for Newton’s 1st
law?
 Law of inertia
 What
does Newton’s 1st law state?
 An object in motion stays in motion and
an object at rest stays at rest unless acted
upon by an unbalanced force
 What
affects the amount of inertia an
object has?
 Mass- More mass= more inertia
 What
has more inertia- a bowling ball or a
tennis ball? How do you know?
 Bowling ball b/c is has more mass
 What
does that mean about changing
the motion of the bowling ball versus the
tennis ball?
 Because the bowling ball has more
inertia, it will be more difficult to change
its motion, so it will need more force
(Newton’s 3rd) if you wanted to achieve
the same acceleration.
 Explain
why a skateboarder going down a
hill would fall forward if he/she were to hit
a rock.
*The team that has the answer with the most
vocabulary correctly used with win these
points
 What
does Newton’s 3rd law state?
 For every action there is an equal and
opposite reaction
 Calculate
how much force would be
needed to accelerate a car that is 350 kg
at a rate of 70 m/s/s.
 24,500 N
 What
 F=ma
is the formula for Newton’s 2nd law?
 Calculate
the acceleration of
snowboarder that comes to a stop in 6
seconds after traveling at a speed of 35
m/s.
 -5.83 m/s/s
 Calculate
the acceleration of an object
that has a mass of 76kg and is being
pushed with a 120 N force.
 1.5 m/s/s
 Calculate
the velocity of a plane that is
traveling from Maine to Florida if it travels
612 miles in 2 hours.
 306 miles/hr
 If
you are pushing a box across the floor,
what happens to the acceleration of the
box if a mass is added and you push with
the same force?
 It decreases
 You
are using a sling-shot to shoot a rock.
After your first trial, you want to make it for
farther. You cannot change the angle
that you aim at. What change could you
make to get the rock to travel farther?
 Pull the rubber band farther back
because it increases the force.


2 students are sitting on skateboards (similar to
our class demonstration). If the larger student
pushes on the smaller student, why does the
smaller student accelerate more than the
larger student?
Because he/she has less mass and according
to Newton’s 3rd law the same amount of force
was acting on both students and Newton’s
2nd law says that objects with less mass
accelerate more with the same amount of
force.
 What
2 possible changes can you make
to increase an object’s acceleration?
 Increase the force or decrease the mass
 What
is the relationship between mass
and gravitational pull?
 More mass=greater gravitational pull
 Other
than mass, what else affects the
amount of gravitational pull?
 Distance




Weight is a force. What should the unit of
weight be?
NEWTONS
Just a reminder: MASS vs WEIGHT
Mass is amount of matter in an object, weight
is a measure of the effect of gravity on an
object. Your MASS NEVER changes. Your
weight can, depending on gravity!
 Use
all of Newton’s Laws to explain the
motion of a baseball that is being hit with
a bat.
 Explain
why a rocket can move through
outer space where there is no matter for it
to push on.
 According to Newton’s 1st law, an object
in motion will stay in motion (same
direction and same speed) unless an
outside force acts upon it. It is already in
motion, so it will continue to do so until
there is an unbalanced force to act on it.
A
hovercraft, which moves over water on
a cushion of air, can achieve greater
speeds that ordinary boats. Explain why
this is possible.
 The air reduces the amount of friction
acting on the boat. Friction is one of the
common unbalanced forces that causes
a change in motion. With less friction,
there is less of a force acting against
motion.
 Use
Newton’s 2nd law to explain why large
trucks get fewer miles per gallon of gas
than smaller cars.
 It takes a greater force to move the larger
truck with the same acceleration as the
smaller car because it has more mass.
According to Newton’s 2nd law, it takes
more force to accelerate an object with
a greater mass.