forces and motion review 8 th grade tag physical science
TRANSCRIPT
Forces and Motion Review
8th Grade TAG Physical Science
Force
Define Force: A push or pull What are the Units of force? N (newton)
How do forces affect the motion of an object?
When forces are balanced, what is the net force?
Net force is = 0 If the net force is 0, how does this relate to
acceleration? No acceleration When forces are balanced, what does this
mean for the objects motion? no change in an objects motion.
How do forces affect the motion of an object?
When an unbalanced force acts on an object, is there a net force?
Yes. Net force > 0 When there is an unbalanced force is there
acceleration? Yes…the object accelerates.
Can on object be moving and still accelerate?
Yes!
Ex: Driving on GA400 at a constant velocity (56 mi/hr), not speeding up, slowing down, or changing direction.
Car is moving, but 0 acceleration, Fnet=0
Friction A force resulting from 2 objects moving past
each other What are the 3 types: Sliding, Rolling, Fluid
Friction
What is friction dependent on? (hint: think of the lab experiment…if you finished) We increased the mass and the resulting force
was increased We changed the surface (table, carpet,
sandpaper,duct tape) and the force changed Coefficient of friction, 0 to 1
If close to 0, very low friction If close to 1, high friction
Friction (cont.)
Friction acts in a direction opposite to motion
Force of Friction=Ffr
Speed vs. Velocity-very similar!
Speed How fast something is going Units of mi/hr or m/s Ex: driving on GA400 at a speed of 65mi/hr Can NOT draw a vector for speed
Velocity The speed of an object in a particular direction Units of mi/hr north or m/s north Ex: driving on GA400 at a velocity of 65mi/hr north (included
direction) Can draw a vector for velocity (since vector shows magnitude
and direction)
Acceleration The rate at which velocity changes over time Units of m/s2
If an object is speeding up, slowing down, turning…there is acceleration
Net force diagram of toy car (fnet):
Car stopped
What is the Net Force?
Fnet = 0
Is car speeding up, slowing down, no change?
No change, so no acceleration
Hand let go, and still rolling across the floor
Is car speeding up, slowing down, no change?
Slowing down, so accelerating (negative or deceleration)
Being pushed across floor
Is car speeding up, slowing down, no change?
Speeding up (so accelerating)
Fnet Fnet
Acceleration (cont)
All objects accelerate toward the earth at the same rate, regardless of their mass
All objects accelerate toward Earth at a rate of 9.8 m/s2
Air resistance (fluid friction) affects some objects more than others (depends on size and shape of object) Fair
FairThe force of gravity is the same for both pieces of paper
Fg Fg
Falling Objects
What happens to the air resistance as the speed of a falling object increases?
Air resistance increases
FairFair
Fg Fg
Falling Objects (cont)
What happens when air resistance of a falling object becomes equal to the downward force of gravity?
Fg = Fair, so Fnet =0 (object stops accelerating…but still moving)
The object is falling at a constant velocity TERMINAL VELOCITY
Fair
Fg
Ex: Toy Car
Drag toy car across the floor at a constant speed
Ffr
Fg
Fn
Fpull
Force of the pull continues to act on the car (hand still touching car)
Which direction is friction acting?
Opposite to motion of car
Is object moving?
Yes
What is Fnet?Fnet = 0Is there acceleration?No (since no change in motion)
Direction of Motion
Ex: Toy Car after it just comes off a ramp.
Direction of motion
Fnet
Force Diagram
Ffr
Fn
Fg
Note: Fn & Fg equal in length but opposite direction
Are the forces Balanced or Unbalanced?
Unbalanced
Is the car speeding up, slowing down or speed not changing?
Slowing Down, so still has acceleration.
Ex: Soccer Ball, rolling on the ground, just after the kick
Direction of motion Remember, there is nothing pushing the ball
forward after the kick, so no more forward force.
Is there an Fnet?
Yes!
How is the ball’s motion changing?
Slowing down
So..is there acceleration?
Yes! (negative acceleration)
Ffr
Fnet
Fn
Fg