Force Review

1
Force Review

• Answers

2
Define Newtons 1st Law

• First Law An object at rest stays at rest or an
  object in motion, stays in motion (in the same
  direction/at the same speed) unless acted upon by
  an unbalanced force
• Also called the law of inertia

3
Define Newtons 2nd Law

• Second law The greater the force applied to an
  object, the more the object will accelerate. It
  takes more force to accelerate an object with a
  lot of mass than to accelerate something with
  very little mass.

4
Define Newtons 3rd Law

• Third law For every action force, there is an
  equal and opposite reaction force. (Forces are
  always paired)

5

• Pete was doing some yard work. He grabs the
  wheelbarrow from the shed pushes it over to a
  pile of rocks to be moved to the back. After
  filling the wheelbarrow, he struggles to lift the
  heavy load. Not seeing the small slope he loses
  control of the wheelbarrow and it drags him down
  the hill.

N 2nd
N 1st
N 3rd
N 2nd
N 2nd law when he pushes wheelbarrow (need force
to push mass)
N 1st law when he moves the wheelbarrow to a pile
of rocks (objects at rest will remain at rest
until an unbalanced force acts upon it)
N 2nd law when he lifts the heavy load (need
force to push mass)
N 3rd law when he loses control and is dragged by
wheelbarrow- and opposite reaction
6
Joey just finished paying for his groceries and
heads to the parking lot. He noticed that it
snowed while in the store requiring more force to
push the cart. While pushing his cart across the
lot he slips on a patch of ice and falls towards
the cart.
N 1st
N 2nd
N 1st and 3rd
N 1st law he pays for groceries and heads to lot-
he changed is state of motion
N 2nd law requires more force to push cart(need
force to push mass)
N 1st and 3rd law he slips and falls (change in
motion-1st law) and falls towards the cart and
opposite reaction.
7
Draw a force arrow diagram that shows the forces
acting on the objects. Be sure to label each
force arrow and carefully draw each arrow the
appropriate size relative to other forces acting
along the same axis.
A bird flying through the air.
Air resistance
Bird
Applied force
Gravity
Reasoning
Air resistance is supporting the birds descent
and gravity is pulling down on the bird. The
applied force is the wing force of the bird
flying.
8
Draw a force arrow diagram that shows the forces
acting on the objects. Be sure to label each
force arrow and carefully draw each arrow the
appropriate size relative to other forces acting
along the same axis.
Cat sleeping in the chair..
Normal
Cat
Gravity
Reasoning
The cat is being supported by the chair which is
normal force and the gravity is pulling on the
chair with cat.
9
Draw a force arrow diagram that shows the forces
acting on the objects. Be sure to label each
force arrow and carefully draw each arrow the
appropriate size relative to other forces acting
along the same axis.
A man pushing a very heavy car off to the side of
the road.
Normal
Car
Applied force
Friction Force
Gravity
Reasoning
The pushing is the applied force which is
slightly bigger than the friction which opposes
the motion of the force because the car does
move. Normal force is the force provided by the
ground and gravity is the downward force.
10
Draw a force arrow diagram that shows the forces
acting on the objects. Be sure to label each
force arrow and carefully draw each arrow the
appropriate size relative to other forces acting
along the same axis.
A woman knocking on the door.
Normal
Door
Applied force
Friction Force
Gravity
Reasoning
The knocking is the applied force which is bigger
than the friction which opposes the motion of the
force. Normal force is the force provided by the
door being mounted to the wall and gravity is the
downward force.
11
Draw a force arrow diagram that shows the forces
acting on the objects. Be sure to label each
force arrow and carefully draw each arrow the
appropriate size relative to other forces acting
along the same axis.
A kid sliding on a slip n slide on a hot summer
day.
Normal
Slip n slide
Friction Force
Gravity
Reasoning
The friction which opposes the motion in this
case sliding. There is no applied force acting
on the kid- just sliding. Normal force is the
force provided by the ground and gravity is the
downward force.
12
Draw a force arrow diagram that shows the forces
acting on the objects. Be sure to label each
force arrow and carefully draw each arrow the
appropriate size relative to other forces acting
along the same axis.
A boy pulling on the string to turn on the light.
Normal
Light
Applied force
Tension
Reasoning
Gravity
The pull on the string is both applied force and
tension force. Normal force is the force
provided by the light supported by the ceiling
and gravity is the downward force.