Acceleration
What is acceleration?
What is the equation?
What is the SI unit?
Acceleration is the rate at which the velocity is changing in relation to time.
a = v/t
m/s2
Describe Friction.
they say: Friction opposes applied forces, Friction slows down the motion, opposes the motion of two objects that are moving past one another.
What is net force?
When all the forces acting on an object are combined
What are the SI unit for Force, mass, and acceleration?
Force: N, mass: kg, a: m/s2
They said: What is the acceleration of a 2.3-kg bag of sugar that drops off a shelf with a force of 22.5 N?
a= f/m = 22.5 /2.3 = 9.78 m/s2
(T/F): Acceleration can be positive or negative.
T: Acceleration can be positive or negative. a = change in velocity over time => the change in velocity could be positive or negative
delta v = vf - vi
Talk about the 4 types of friction.
Static Friction, Sliding Friction, Rolling Friction, Fluid Friction
they say: Static means unmoving or at rest. Static friction acts in the direction opposite the direction of the applied force. Sliding Friction: Once the two objects that are in contact start to move past one another. Rolling Friction: Rolling friction occurs after a round object has overcome the static friction of the surface it is on and begins to roll. Fluid Friction: Fluid friction occurs whenever an object is moving through a fluid such as a mixture of gases, the air we breathe, or water.
When do we add forces? When do we subtract forces?
Adding forces: when they are in the same direction.
Subtracting forces: when they are in opposite directions.
Talk about the what they call the 3 Newton's laws
They say: Law of inertia: objects in motion will remain in motion, and objects at rest will remain at rest unless acted on by an unbalanced force.
Newton's second law: f = ma, the acceleration of an object is directly proportional to the net force acting on an object in the direction of the force and is inversely proportional to the object's mass.
Third law: Newton's third law of motion states that for every action, there is an equal and opposite reaction.
They said: What net force would be required to give a mass of 53.50 kg an acceleration of 4.16 m/s/s.
f= m*a = 53.5 * 4.16 = 222.56 N
(Y/N): Accelerating does not mean an object is moving faster.
Yes: It means that either the speed, direction, or both are changing.
The speed can change by going faster or slower, but regardless of the speed going faster or slower, the object is still accelerating.
When is the net force = zero?
When the forces are equal in magnitude and opposite in direction
How do you change an object's mass?
By adding or removing
They said: A Chihuahua tugs on a rope with an acceleration of 1.5 m/s2 and a force of 3 N. What is the mass of the dog?
m= f/a = 3/1.5 = 2 kg
Acceleration is affected by the change in 3 things:
Speed
direction
Speed and direction
When are the forces balanced?
When the forces acting on an object are equal in magnitude but opposite in direction, they are balanced.
They say: You and a friend are sliding a large 100-kg box across the floor. Your friend adds a box on top with a mass of 50 kg. The box has an acceleration of 2.0m/s2 to the right. What is the force that you exert on the box?
a= 2 m/s2
f=?
m= 100kg + 50kg = 150 kg
f=m*a = 150* 2 = 300 N
They said: If there is a block of mass 2kg, and a force of 20 N is acting on it in the positive x-direction, and a force of 30 N in the negative x-direction, then what would be its acceleration?
Fnet = 20-30 = -10 N
a=f/m = -10/2 = -5 m/s2
How do you represent a graph of acceleration?
Describe the graph of acceleration in the following cases:
Positive acceleration, Negative acceleration, Zero Acceleration.
How can you calculate the acceleration from a graph?
velocity-time: velocity on the y-axis, time on the x-axis
Positive acceleration: increasing line
Negative acceleration: decreasing line
Zero acceleration: parallel to the x-axis
a = slope = change in y/change in x
When are the forces Unbalance?
when the opposing forces acting on an object are not equal in magnitude
when forces acting on an object act in the same direction
What is the equation of weight, what is the unit?
They say that w = mg, weight is in N
They said: You and a friend are sliding a large 100-kg box across the floor. Your friend pulls to the right with a force of 250N. You push to the right with a force of 300N. The frictional force of the floor opposes the motion with a force of 500N. What is the acceleration of the box.
Fnet = (250+300) -500 = 550-500 = 50 N
a=f/m = 50/100 = 0.5 m/s2