Download Force and Motion PPT

Newton’s Laws of Motion
• Newton has three laws that explain the
way things move.
Newton’s First Law
• Newton’s 1st Law – the Law of Inertia- An
object at rest will stay at rest unless acted
on by an unbalanced force. An object in
motion will stay in motion (in the same
direction and at the same speed) unless
acted on by an unbalanced force.
Newton’s Second Law
• Force = Mass x Acceleration
• The heavier an object is, the more force
required to move it.
Newton’s Third Law
• For every action there is an equal and
opposite reaction
Newton’s 1st Law
• The soccer ball stays at rest until the
player kicks it- it moves until the grass, or
another player stops it
Newton’s 2nd Law
• It would take more force to move an
elephant than it would to move a mouse
Newton’s 3rd Law
• The gases coming out of the rocket push
on the atmosphere which pushes back at it
with equal and opposite reaction –
allowing the rocket to move into space
How far you travel along a path
while you change position is….
Speed is the distance an object moves in a
certain amount of time.
Speed = Distance
Time
We use speed to measure the
motion of objects.
An object may be moving at a slow
rate or at a fast rate.
A horse can run 120 meters in 6
seconds.
What is the speed of the horse?
Velocity
Speed of an object in a given direction.
Different from speed because speed only tells
how fast an object is moving. Velocity
includes both speed and direction.
Example: a plane’s velocity is 6000km/h south
• Tells how fast an object changes its velocity.
When an object is speeding up, it is
accelerating.
• When an object is slowing down it is also
accelerating. Slowing down is sometimes called
negative acceleration or deceleration.
• An object is not accelerating when it travels in a
straight line at a constant speed or when it sits at
rest.
• A train sitting in a station (is or is not)
accelerating.
• Traveling at 100km/hr on a straight stretch
of track (is, is not) accelerating
• Pulling out of the station?
• Slowing down as it pulls into a station?
Force and motion describe
everyday things that are happening
all the time.
1. Did you pick up a pencil?
2. Did you turn a page?
3. Raise your hand?
4. Pack your backpack?
All these are examples of force and
motion!
• Change in position relative to fixed objects
• Moving from one place to another
• An object an observer uses to detect
motion.
• Push or pull
• When you throw a baseball , you are
pushing it through the air.
• When you pick up a baseball you are
pulling it up from the ground.
To describe a force, we must know
two things.
Its SIZE
AND
Its DIRECTION.
• The force being applied by each team in a
tug of war game is in opposite directions.
Red team pulls to the right . Yellow team
to the left. Suppose that the force applied
by each team is equal in size. Then each
team is pulling equally hard, but in
opposite directions.
• Will the rope move?
Balanced forces: Two forces
that are equal in size and
opposite in direction.
When balanced forces act on an object at
rest, the object does not move.
Balanced Force
• Push as hard as you can against a solid
brick wall. The wall doesn’t move. It
pushes back with a force equal in size and
opposite in direction to your push.
Unbalanced forces
Change the motion of the object they act
upon.
1. Can make an object speed up
2. Can make an object slow down
3. Can change the object’s direction
In tug of war what would happen if two
members of the yellow team fell down and
let go of the rope?
The forces would not be balanced. The size
of the force of the red team would be
greater.
Types of Forces
•
•
•
•
•
Contact
Friction
Gravitational
Magnetic
Electrical
What is the difference between
socks and sneakers?
• Sneakers have a lot more friction than
socks
• In your socks you can slide a long way
down the hall.
• In your sneakers you can get a running
start and stick to the floor.
• Happens when two things rub together.
• Makes it difficult for an object to move
across a surface
• Effect is usually to slow you down.
• Will a car move faster on a smooth surface
or a rough surface?