Chapter 10- Forces
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What is a force?
What is the unit for force?
What is a net force?
What is the difference between
unbalanced and balanced
forces?
NOTES WRITTEN
Force– a push or pull
 SI unit for force is a Newton (kg ° m/s2 )
 Forces are described by their magnitude and direction
Net Force– the combination of all forces acting on an object
 If one force is greater than the other force the overall movement is in
the direction of the greater force
Unbalanced forces – force that causes the velocity of an object to
change because the forces are not balanced
 When two or more forces act in the same direction, you add
 When forces act in opposite directions, you subtract
Balanced forces – equal forces acting on one object in opposite
directions (so no movement occurs)
 When equal forces are exerted in opposite directions, the net force is
zero
What is friction?
Friction – the force that one surface exerts on another when the two
rub against each other
 Friction acts in the opposite direction of an object’s motion
 The strength of the force of friction depends on two factors:
1) types of surfaces involved
2) how hard the surfaces rub against each other
What are the four types of
friction?
SUMMARY
Four types of friction:
Sliding friction – friction of two solid surfaces sliding over each other
Rolling friction – friction of an object rolling over a surface
Fluid friction – friction of an object moving through a fluid
Static friction – friction of an object is at rest
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What is gravity?
NOTES WRITTEN
Gravity – the force that pulls objects towards each other
 force of gravity between objects increases with greater mass and
decreases with greater distance
Mass – the measure of the amount of matter in an object
Weight – mass x acceleration due to gravity (9.8 m/s2)
How does air resistance
effect free fall?
Free fall – when the only force acting on an object is gravity
Air resistance – fluid friction experienced by objects falling through air
 Air resistance is a force in the opposite direction of the object
 Air resistance is not the same for all objects (depends on surface area)
 Projectile (an object that is thrown horizontally) will fall at the same
rate as an object thrown vertically
What is the difference between
compression and tension?
What is Newton’s first law?
Matter is considered elastic if it returns to its original shape after
it is stretched or squeezed
Compression – an elastic force that squeezes or pushes matter together
Tension – an elastic force that stretches or pulls matter
Newton’s First Law of Motion – an object at rest will remain at rest, and an
object that is moving at constant velocity will continue moving at constant
velocity, unless acted upon by and unbalanced force (called the law of
inertia)
 The amount of inertia an object has depends on its mass –
the greater the mass the greater the inertia
 Inertia– the tendency of an object to resist change in its motion
What is Newton’s second
law?
Newton’s 2nd Law – acceleration depends on the net force acting on an
object and on the object’s mass (force = mass x acceleration)
The net force on an object is equal to the product of its acceleration & mass
 Force = Mass x Acceleration
 Acceleration = Force / Mass
 Mass = Force / Acceleration
SUMMARY
Chapter 10- Forces (page 2)
CUE WORDS or QUESTIONS
NOTES WRITTEN
Newton – the force required to accelerate one kilogram of mass
at 1 meter per second per second (kg.m/s2 is a Newton)
What is Newton’s third law?
Newton’s 3rd Law of Motion – if one object exerts a force on another
object, then the second object exerts a force of equal strength
in the opposite direction on the first object (action- reaction pairs)
Newton called one force an action, and the other he called a reaction
What is momentum?
Momentum is the ‘quantity of motion’ (momentum = mass x velocity)
Law of Conservation of Momentum states that the total momentum of the
objects that interact does not change (momentum is not lost)
The total momentum of any group of objects remains the same unless
outside forces act on the objects (such as friction)
When two objects collide in the absence of friction, momentum is not lost
SUMMARY