Friction and Gravity
Name four types of friction
Sliding, Rolling, Fluid, and Static
What is Newton's second law?
Fnet = ma
The formula to calculate momentum
p = mv
The gravitational acceleration of Earth:
9.81 m/s2 towards Earth
The name of the upward force exerted on objects by fluids
Buoyant force
The two factors that affect gravitational attraction of objects
Mass and Distance
An object's resistance to a change in motion:
Inertia
An object with a mass of 0.5 kg travels at a velocity of 20 m/s. Calculate its momentum:
p = mv
p = 0.5 x 20
p = 10 kg m/s
Satellite
If the weight of an object is greater than the buoyant force pushing upward, the object will:
Sink
The two factors that affect the force of friction
The types of surfaces involved
How much force is applied to those surfaces (how hard the surfaces are pushed together)
A cannon fires a cannonball. Explain what happens to the cannon immediately after firing and explain why.
The cannon would accelerate backwards, because Newton's 3rd Law states that every force action has an equal and opposite force reaction. The cannon pushes out the cannonball, but the cannonball also pushes back on the cannon
Explain how objects traveling at the same velocity could have different momentum:
Two objects traveling at the same velocity could have different momentum if their masses are different.
p = mv
When forces cause objects to move in circular motion, we describe that force as being:
Centripetal, or center-seeking
If the weight of an underwater object is equal to that of the buoyant force, the object will:
Stay in place
Net force = 0 , object will not accelerate in any direction
The law that states that the force of gravity acts between all objects in the universe that have mass.
The Law of Universal Gravitation
Rocket ships accelerate in outer space even though there is no matter in space for the rocket to push off of. Explain how the rocket is able to accelerate:
The rockets burn fuel and produce gas which is pushed backward out of the rocket. When the rocket pushes out the gas, the gas pushes back on the rocket according to Newton's 3rd Law, resulting in a Net force causing the rocket's acceleration.
The total momentum of a system before any interactions is 312 kg m/s. Multiple objects within the system begin colliding with one another, changing the velocities of the objects in the system. Calculate the total momentum of the system after the collisions and explain why:
312 kg m/s because momentum is conserved before and after interactions
The gravitational acceleration of a planet is 20 m/s2. What would an object's speed be if it were in free fall for 5 seconds on this planet? (Assume no air resistance/fluid friction)
100 m/s
A fluid has a volume of 2.5 L. An object with an unknown volume of is placed into the fluid. The fluid rises to 3.0 L. What is the volume of the object?
500 mL or 0.5 L
The gravitational strength of the moon is about 1/6th that of the Earth. If a person with a mass of about 54 kg weighs 120 pounds on Earth, what would be their weight on the moon? What would be their mass on the moon?
Weight on the moon = 20 pounds
Mass = 54 kg
Describe what would happen to Earth's orbit if the sun instantly vanished, and explain why.
In the absence of the sun's gravitational pull, the Earth would no longer orbit in a circle, but would continue moving through space in a straight line because of Newton's first law of motion and Earth's inertia.
In a sticky collision, an object with a mass of 10 kg travels with a velocity of 10 m/s. It collides with a second object with a mass of 40 kg which is at rest. What is the velocity of the objects after they collide?
pbefore = 10 kg x 10 m/s
pbefore = 100 kg m/s
pbefore = pafter
100 kg m/s = 50 kg x vafter
vafter = 2 m/s
Name 3 examples of objects that undergo circular motion, and name the centripetal forces of each:
A tetherball swinging around a pole - the rope pulling on the ball is centripetal
The moon orbiting around Earth - the gravitational force is centripetal
Standing on a merry-go-round - the frictional forces are centripetal
Density = Mass / Volume
Density = 2g/4cm3
Density = 0.5 g/cm3
Yes, the object will float because it is less dense than water is.