Transcript Motion and Forces Ch 2

Forces Change
Motion 2.1
Phoenix Science 2010
Force
• A push or a pull
Types of Forces
Contact Forces
- friction
Non-Contact Forces
- gravity
- magnetic
Contact Force
• When one object pushes or pulls another
object by touching it.
Gravity
• the universal force of attraction between
two masses. (non-contact)
Friction
• a force that resists motion between two
surfaces that are pressed together.
(contact)
Net Force
• All of the forces acting upon an object
combined.
• Balanced forces cannot change an object’s
motion.
• Unbalanced forces are needed to change
an object’s motion.
Newton’s First Law
• INERTIA
– Objects at rest, stay at rest, and objects in
motion, stay in motion, with the same velocity
unless acted upon by an unbalanced force.
Inertia
• Resistance of an object to change in its
motion.
Force and Mass
determine
acceleration 2.2
Phoenix Science 2009
Newton’s 2nd Law
• Acceleration of an object increases with
increased force and decreases with
increased mass.
• What 3 concepts are involved here?
Force = m x a
• Force = mass x acceleration
• F = ma
• Force is measured in Newtons
– ex. Force = 40 N
Math to blow your mind
• Acceleration = Force / mass
• Mass = Force / acceleration
• I’ve got to show you this on the board.
• Don’t worry if you don’t get it the first time.
2.3 Forces act in
pairs
Phoenix Science 2008
Newton’s 3rd Law
• Every time an object exerts a force on
another object, the second object exerts a
force that is equal in size and opposite in
direction back on the first object.
• Action – Reaction Pairs.
Newton’s 3 Laws
describe and predict
motion.
• Reread p. 61
2.4 Forces transfer
momentum
Phoenix Science 2008
Momentum
• a measure of mass in motion
• p=mv
• measured in kg * m/s
Collision
• a situation in which two objects in
close contact exchange energy and
momentum.
• read about the two types on p. 68.
conservation of
momentum
• the total momentum of a system of
objects does not change, as long as
no outside forces are acting on that
system.
• Another way of looking at Newton’s
3rd Law.
air resistance
• friction due to air molecules, also
referred to as drag.
• Solve for force:
• m = 75 kg, a = 3 m/s²
• Solve for force:
• m = 4 kg, a = 6 m/s²
• Solve for acceleration:
• F = 45 N, m = 15 kg
• Solve for force:
• m = 5 kg, a = 8 m/s²
• Solve for mass:
• F = 75 N, a = 5 m/s²
• Solve for acceleration:
• m = 15 kg, F = 60 N
• Solve for mass:
• F = 12 N, a = 6 m/s²
• Solve for mass:
• F = 220 N, a = 11 m/s²
• Solve for force:
• m = 70 kg, a = 5 m/s²
• Solve for Momentum:
• m = 1.5 kg
v= 2 m/s
• Solve for Momentum:
• m = 20 kg
v= 30 m/s
• Solve for Momentum:
• m = 0.5 kg
v= 0.25 m/s
• Solve for Momentum:
• m = 15 kg
v= 1.5 m/s