Transcript Combining Forces

2.1 Combining Forces
force
contact force
noncontact force
net force
unbalanced forces
balanced forces
Newton’s first law of motion
2.1 Combining Forces
Force
• When more than one force acts on an
object, the combined effect is caused by
the sum of all applied forces.
• A push or a pull on an object is a force.
2.1 Combining Forces
Contact and Noncontact Forces
• A contact force is exerted only when two
objects are touching.
• A noncontact force is exerted when two
objects are not touching.
• Magnets exert a noncontact force on
each other.
2.1 Combining Forces
Force is a Vector
• Vectors have magnitude and direction.
• Force has a direction and a magnitude.
• Force is measured in Newtons.
2.1 Combining Forces
Combining Forces
• When more than one force acts on an
object, the forces combine.
• The combination of all the forces acting on
an object is called the net force.
2.1 Combining Forces
Combining Forces in
the Same Direction
• Forces are vectors and require a reference
direction.
• When forces in the same direction combine,
the net force is in the same direction and the
size of the force is the sum of the forces.
2.1 Combining Forces
Combining Forces in
the Same Direction (cont.)
• If two people push the dresser to the right,
the forces are added together.
2.1 Combining Forces
Combining Forces in
Opposite Directions
• When forces in opposite directions
combine, the net force is in the direction
of the larger force.
• The size of the net force is the difference
between the two forces.
2.1 Combining Forces
Combining Forces in
Opposite Directions (cont.)
• Two people exerting a force in opposite
directions show how vectors combine to
create net force.
2.1 Combining Forces
Unbalanced and Balanced Forces
• If the net force on an object is not zero, it
is an unbalanced force.
• If the net force on an object does equal
zero, it is a balanced force.
2.1 Combining Forces
Balanced Forces
2.1 Combining Forces
Balanced Forces and Motion
• If two people push with the same force,
the dresser does not move.
• The forces have the same magnitude.
• The forces are in opposite directions.
• The net force on the dresser is zero and
the forces are balanced.
• The motion of the dresser does not
change.
2.1 Combining Forces
Unbalanced Forces and Motion
• Unbalanced forces change motion.
• If two people push with different force, the
dresser moves.
• The forces have a different magnitude and
are in opposite directions.
• The net force on the dresser is not zero
and the forces are unbalanced.
• The dresser moves in the direction of the
larger force.
2.1 Combining Forces
Newton’s First Law of Motion
• If the net force on an object is zero, the
velocity of the object does not change.
• If the net force is zero and the object is at
rest, it remains at rest.
• If the net force is zero and the object is
moving, it continues to move in a straight
line with constant speed.
Newton’s Laws
of Motion
2.1 Combining Forces
Inertia and Mass
• Mass is the amount of matter in an object.
• The more mass an object has, the more
inertia it has and the harder it is to change
its motion.
• A bicycle is easier to push than a car
because it has less mass.
2.1 Combining Forces
Which of the following changes
occur when an unbalanced force
acts on an object?
A motion
B mass
C inertia
D weight
2.1 Combining Forces
What is the net force acting on a
door if one person pushes to the
right with a force of 2000 N and a
second person pushes with a force
of 1500 N to the right?
A 3500 N to the right
B 3500 N to the left
C 500 N to the left
D 500 N to the right
2.1 Combining Forces
You are riding a bike. In which of the
following situations are the forces
acting on the bike balanced?
A You pedal to speed up.
B You turn at constant speed.
C You coast to slow down.
D You pedal at constant speed.
Balanced & Unbalanced Forces
• Balanced Skateboard
Forces
• Unbalanced Skateboard
Forces
• Draw the skateboard and
the vectors in each
direction to cause
balanced forces.
• Draw the skateboard and the
vectors in each direction to
cause unbalanced forces.
• Balanced Frisbee Forces • Unbalanced Frisbee
Forces
• Draw the frisbee and the
vectors in each direction to • Draw the frisbee and the
cause balanced forces.
vectors in each direction to
cause unbalanced forces.