Vocabulary
What are the 3 ways in which velocity can change?
1. Change in speed
2. Change in direction
3. Change in speed and direction
A train travels a total distance of 750 km in 3 h. What is the speed of the train?
s = d / t
s = 750 km / 3 h
s = 250 km/h
For every action there is an equal and opposite reaction
Draw an example of a speed-time graph that represents an object slowing down and coming to a stop. Include correctly labeled x-axis and y-axis.
X-axis = time (s)
Y-axis = speed (m/s)
A line with an downward slope, end touching the x-axis
What is the difference between constant speed and instantaneous speed?
Constant speed is when an object travels the same distance each second, while instantaneous speed is a speed taken at a specific time (changing speed).
What is the velocity of a person that hopped 10 m to the right in 2.5 s?
s = d/t
s = 10m / 2.5s
s= 4 m/s
4 m/s to the right
What is Newton's Second Law?
The net force acting on an object is equal to the object’s mass times the acceleration of the object
net force = mass x acceleration
F = m x a
What is a reference direction?
Provide an example of a reference direction using left and right as your directions.
The direction you choose from a starting point to describe an object’s position
Ex) to the right is positive; to the left is negative
What is the definition of Inertia?
The tendency of an object to resist a change in its motion
A car is driving North on a highway. At 6 seconds it is traveling at 20 m/s. It then speeds up and at 10 seconds it is still traveling North but now at a speed of 32 m/s. What is the acceleration of the car?
a = (vf-vi) / t
a = (32 m/s - 20 m/s) / (10 s - 6 s)
a = 12 m/s / 4 s
a = 3m/s2
What is Newton's First Law of Motion? (include both parts)
An object at rest tends to stay at rest unless acted upon by an outside force.
AND
An object in motion tends to stay in motion unless acted upon by an outside force
Explain how the gravitational force between two marbles (both at a mass of 10g) would be affected if you increase the mass of marble A to 20g, but the mass of the marble B stays at 10g. Why?
The gravitational force between the marbles would increase because the mass of at least one marble increased
What are the 3 ways in which acceleration can change?
1. Speeding up
2. Slowing down
3. Changing direction
An object with a mass of 5.0 kg accelerates 8.0 m/s^2 when an unknown force is applied to it. What is the amount of the force?
f = 5.0kg x 8.0 m/s^2
f = 40 N
You release a toy car down a ramp. The car eventually stops after rolling down the ramp. Which of Newton's Laws explains why the car stops?
Newton's First Law
(An object in motion stays in motion unless acted upon by an outside force. Sliding friction is the force acting against the motion of the car causing it to stop)
Draw an example of a distance-time graph for an object that speeds up for 4 seconds, stops for 2 seconds, then speeds up for 3 seconds. Include correctly labeled x-axis and y-axis.
x-axis = distance (m)
y-axis = time (s)
An increase in slope from 0s-4s, a horizontal line from 4s-6s, an increase in slope from 6s-9s
Newton's Third Law
An object with a mass of 2300g has a force of 10N applied to it to push it to the right. There is sliding friction acting against the motion to the left at a force of 0.8N. What is the acceleration of the object?
f = m x a
a = f / m
net force (f) = 10N - 0.8N = 9.2N
mass (m) = 2300g/1000 = 2.3kg
a = 9.2N / 2.3kg
a = 4 m/s^2
An in-line skater uses two hands to push against a wall in front of her. Explain why she rolls backward.
The skater exerts an action force on the wall; the wall exerts a reaction force of equal size but in the opposite direction on the skater.
The reaction force is greater than the force of static friction on the skater, so the skater rolls backward, away from the wall.
What are the 3 types of friction? Provide an example for each
Static Friction: If you push on a boulder alone, static friction would be the force opposing you if you are unable to move the boulder (it stays stationary even when you push on it)
Sliding Friction: If you and a friend push on a boulder together and it moves forwards, sliding friction would be the force opposing you trying to stop it from moving
Fluid Friction: If you drop a piece of paper, gravity is the force pulling the paper down towards the ground and fluid friction in the form of air resistance is pushing up on the paper trying to stop the paper from falling