2 pt 3 pt 4 pt 5pt 1 pt 2 pt 3 pt 4 pt 5 pt 1 pt 2pt 3 pt 4pt 5 pt 1pt 2pt 3 pt 4 pt 5 pt 1 pt 2 pt 3 pt 4pt 5 pt 1pt Measuring Motion What is Force? FrictionGravity Newton’s Laws and Momentum
What is an object that appears to stay in place and helps you detect motion in another object called?
Reference Point
How do you calculate average speed?
Distance ÷ Time
What is the difference between speed and velocity?
Velocity includes a reference direction.
How do you calculate average acceleration?
Final velocity – starting velocity Time it takes to change velocity
What is the average acceleration of a subway train that speeds up from 9.6 m/s to 12 m/s in 0.8 s on a straight section of track?
3 m/s 2
Which of the following may happen when an object receives unbalanced forces? a.The object changes direction b.The object changes speed c.The object starts to move d.All of the above
The combination of all of the forces acting on an object is the ______.
Net Force
A boy pulls a wagon with a force of 6 N east as another boy pushes it with a force of 4 N east. What is the net force?
10 N east
A dog pulls a rope with a force of 10 N to the left as another dog pulls with a force of 12 N to the right. What is the net force on the rope?
2 N to the right
When finding net force, why must you know the directions of the forces acting on an object?
If you don’t know the direction of the forces you won’t know if you should add the forces or subtract them to find the net force.
Which is an example of friction that is helpful? a.car engine parts wearing out b.tires moving a car forward c.holes developing in your socks d.the erosion of soil by wind
b. Tires moving a car forward
When a mover puts furniture on wheels, which type of friction is the mover using to make the job easier? a.static friction b.sliding kinetic friction c.rolling kinetic friction d. gravitational friction
Rolling kinetic friction
Why does friction occur?
Microscopic hills and valleys between two touching surfaces stick to each other.
What are the two different types of friction?
Kinetic and Static Friction
Describe a situation in which static friction is useful.
Ex. When you’re leaning against a table you don’t want it to slide out from under you.
What is the acceleration due to gravity?
9.8 m/s/s or 9.8 m/s 2
How do you calculate the change in velocity of a falling object?
∆v = g x t
Will air resistance have more effect on the acceleration of a falling leaf or the acceleration of a falling acorn?
Air resistance will have more of an effect on the acceleration of a falling leaf.
What gives an object in projectile motion its vertical motion?
The force of gravity pulling it toward the surface of the earth.
A rock at rest falls off a tall cliff and hits the valley below after 3.5 s. What is the rock’s velocity as it hits the ground?
3.5 s x 9.8 m/s 2 = 34.3 m/s
What does Newton’s first law of motion say about objects at rest and objects in motion?
Objects at rest stay at rest and objects in motion stay in motion unless acted on by an unbalanced force.
What is the relationship between the force on an object and the object’s acceleration?
The acceleration of an object increases as the force exerted on the object increases.
What force is necessary to accelerate a 70 kg object at a rate of 4.2 m/s 2 ?
F = 70 kg x 4.2 m/s 2 = 294 N
What does Newton’s Third Law of Motion state?
Newton’s 3 rd Law: Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.
What is the momentum of a 6 kg bowling ball that is moving at 10 m/s down the alley toward the pins?
p = 6 kg x 10 m/s down the alley = 60 kg●m/s down the alley