Student notes are shown in blue Force Defined Any influence that can cause a change in an objects motion A bat strikes the ball with a force that causes the ball to stop and then move in the opposite direction ID: 645949
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Slide1
Introduction to Forces
Guided Discussion
Student notes are shown in blue.Slide2
Force Defined
Any influence that can cause a change in an object’s motion.
A bat strikes the ball with a force that causes the ball to stop and then move in the opposite direction.Slide3
Force Defined
A push or pull that one object exerts on another
Has a size and direction
Measured in
newtons (N)
You have to apply a force of about 3 N to lift a full can of soda.Slide4
What is a Newton?
Forces are measured in
Newtons
.
One newton is equal to the amount of force needed to accelerate a 1 kg mass 1 m/sec2.In other words, a kilogram mass exerts about 9.8 newtons of force. To put that in perspective, about half of one of Isaac Newton's apples would exert 1 N of force.Newtons are relatively small.http://chemistry.about.com/od/chemistryglossary/g/Newton-Definition.htmSlide5
Net Force
The combination of all forces on an
object
Forces are represented by Arrows. Greater forces are represented by longer arrows. Arrow thickness can also be used to show force.
When multiple forces act on the same object at the same time, the forces are combined to form the net force.Slide6
Balanced and Unbalanced Forces
In a tug of war, each side exerts a force on the ground. If the opposing forces on the ground are equal, they are balanced and the people do not move.
If one of the forces on the ground is greater than the other, the forces are unbalanced and the people move in the direction of the greater force.
Balanced Forces: No Acceleration
Unbalanced Forces: AccelerationSlide7
Balanced Forces
Do not change motion
Cancel each other
Combine
to produce a net force of zeroDo not have the same strength (size)Cause acceleration
Unbalanced ForcesSlide8
Friction
Friction is a force that stops objects from sliding against each other.
The amount of friction between two objects depends on what the materials are made of.
Rule of Friction – Friction always acts in a direction to oppose motion.Slide9
Friction
Examples:
If you push a solid block along the floor to the right, the force of friction on the block will be to the left.
A boat propelled to the east by its motor experiencing water friction to the west
When an object falls downward through the air, the force of friction (air drag or air resistance) acts upward.
PUSH
FRICTION
AIR RESISTANCE
WEIGHTSlide10
Friction
Unbalanced forces:
acceleration
Balanced forces:
constant speed
Balanced forces:
no motion
A
When a car is accelerating, the forces are unbalanced. The force moving the car forward is greater than the opposing force of motion.
B
When a car is cruising at constant speed, the forces moving the car forward is balanced by the force of friction.
C
This car does not roll because the force of friction between the brakes and the wheels balances the force of gravity.Slide11
Friction
Static Friction
– The frictional force that acts on stationary objects when trying to move them.
Sliding Friction
– The frictional force that acts on a moving object, causing it to slow down.Rolling Friction – The static frictional force between the ground and the wheel as it rolls.Fluid Friction – The frictional force an object experiences as it moves through a gas or liquid.Slide12
Air Resistance (also called Fluid Friction)
A type of frictional force that opposes the motion of objects that move through the air
Causes objects to fall with different accelerations and different speeds
Acts in the direction opposite to the velocity of an object moving in air
Size of the force depends on the size and shape of the objectSlide13
Air Resistance
The flying squirrel increases its area by spreading out. This increases air resistance and decreases the speed of its fall.
It appears that a pieces of paper falls slower than a book because it is smaller, but the real reason is the piece of paper is effected by air resistance.Slide14
Terminal Velocity
Objects fall because gravity is pulling them down to the
ground. Because gravity accelerates objects, objects
will keep increasing in speed. The faster the objects
travel, the more they are effected by air resistance.When the upward air resistance force equals the downward force of gravity, terminal velocity is reached – the velocity becomes constant.Slide15
Terminal Velocity
Affects objects differently based on the objects size, shape, and mass of the object
Terminal velocity is reached for the sky diver when air resistance balances the downward force of gravity.