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7th grade year > science force and motion > Flashcards

science force and motion Flashcards

1
Q

state the law of universal gravitation

A

the force of gravity acts between all objects in the universe

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2
Q

what is weight

A

a measure of gravitational pull, measured in Newtons

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3
Q

Why do scientists prefer to describe matter by its mass instead of its weight?

A

weight changes with location

mass doesn’t change

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4
Q

What two factors affect the strength of gravity?

A

mass and distance

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5
Q

How do mass and distance affect gravitational pull?

A

more mass = more gravitational pull

the farther apart, the less the gravitational pull

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6
Q

Compare and contrast balanced and unbalanced forces. 4 contrasts and 2 similarities

A

contrasts: 1. balanced forces are equal (net force = zero) while unbalanced forces are not equal (net force doesn’t = zero). 2. balanced forces do not change notion of an object while unbalanced forces do change an object’s motion.
similarities: 1. push or pull 2. strength and direction

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7
Q

Explain static friction.

A

friction that acts on objects that are not moving - need an unbalanced force to start the motion of stationary objects- the heavier the object, the more static friction

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8
Q

Give an example of static friction.

A

trying to move a stalled car to the side of the road

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9
Q

Explain sliding friction.

A

occurs when two solid surfaces slide over one another - caused by microscopic roughness of all objects - lubricants can reduce sliding friction

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10
Q

Give an example of sliding friction.

A

throwing sand on ice to get friction for walking or driving

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11
Q

Explain fluid friction.

A

fluid friction is when a solid object moves through a fluid (gas or liquid) - easier to overcome than sliding friction

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12
Q

Give an example of fluid friction.

A

water on a water slide

oil on a squeaky hinge

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13
Q

Explain rolling friction.

A

occurs when an object rolls across a surface - easier to overcome than sliding friction because it reduces the amount of contact between surfaces due to its curved shape

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14
Q

Give an example of rolling friction.

A

wheels or ball bearings

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15
Q

How is force described?

A

by its strength and direction

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16
Q

What is a net force?

A

a combination of all forces acting on an object

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17
Q

How can you find the net force if the two forces are in opposite directions?

A

subtract

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18
Q

Define Newton’s 1st Law of Motion.

A

an object at rest will stay at rest,and an object moving at a constant velocity (motion) will continue to move at a constant velocity (motion) unless acted upon by an unbalanced force. Law of Inertia

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19
Q

Define Newton’s 2nd Law of Motion.

A

The acceleration of an object depends upon the object’s mass and the net force acting on the object. Acceleration = force/mass

20
Q

Define Newton’s 3rd Law of Motion.

A

For every action there is an equal and opposite reaction.

21
Q

When an object speeds up, slows down, or changes direction, why is an unbalanced force involved?

A

You have to have unbalanced force to cause motion.

22
Q

Draw the equation triangle for force, mass, and acceleration.

A

force

mass acceleration

23
Q

The force of gravity causes all objects near Earth’s surface to accelerate how fast?

A

9.8m/s or 32 feet/s

24
Q

What is the SI unit for acceleration?

A

m/s meters/second

25
Q

What is the SI unit for force?

A

N (newtons)

26
Q

What is the SI unit for mass

A

kilogram kg

27
Q

What two factors affect the force of friction?

A

types of surfaces involved

how hard the surfaces are pressed together

28
Q

Identify one product of friction.

A

heat
wears surfaces down
slows movement

29
Q

Two children are moving a wagon full of baseball equipment that has a mass of 35kg. One child pulls with a force of 35N, and the other pushes with a force of 60N. The frictional force between the wagon and the ground is 20N. WHat is the net force acting on the wagon? What is the forward acceleration of the wagon? Show your work.

A

35N + 60N = 95 N

95N - 20N = 75N of net force

acceleration = 75N/35kg
acceleration = 2.1m/s
30
Q

Identify the action-reaction forces involved in walking.

A

action - foot pushes down and back on the ground

reaction - the ground pushes your foot up and forward

31
Q

Identify the action-reaction forces involved in paddling a kayak.

A

action - the paddle pulls the water backward

reaction - the water pushes back on the paddle causing the kayak to move forward

32
Q

What is the net force acting on a .15 kg hockey puck accelerating at 12m/s?

A 
force = mass times acceleration
F = 0.15kg X 12m/s 
F = 1.8 N
33
Q

Using Newton’s 2nd Law, what are two ways to increase acceleration?

A

decrease mass or increase force action on the object

34
Q

Define centripetal force.

A

Any force that causes an object to move in a circular path, a center-seeking force

35
Q

How does gravity affect objects that are moving horizontally.

A

Gravity pulls objects toward the center of the Earth

36
Q

Why can objects have a constant speed and still be accelerating?

A

can change directions

37
Q

Define inertia.

A

the tendency of an object to resist a change in its direction

38
Q

How is mass related to inertia?

A

more mass means more inertia

39
Q

Give an example of inertia.

A

It’s easier to move an aquarium without water because adding water adds more mass and makes it harder to move.

40
Q

How does Newton’s 1st Law explain what happens to passengers in a car that suddenly stops.

A

When the car stops, the person’s body is still moving in a straight line due to its inertia. If the person doesn’t wear a seatbelt, they could hit the windshield or dash.

41
Q

Define momentum.

A

a description of an object’s mass and velocity

42
Q

Which is easier to stop, a baseball moving at 20m/s or a car moving at 20m/s? Which has more momentum? Explain.

A

The baseball is easier to stop because it has less momentum. They are moving at the same speed, but the baseball has less mass.

43
Q

Would an arrow shot from a bow have more or less momentum than the same arrow thrown by a person? Explain.

A

The arrow shot from a bow would have moremomentum because it would have a higher velocity even though they both have the same mass.

44
Q

When a rocket is launched, are the forces acting on it balanced or unbalanced? Explain how you know.

A

unbalanced - It moves.

45
Q

Draw a diagram of the motion of a satellite around Earth. Label the forces acting on it. Is it accelerating?

A
  1. gravitational force - toward center of Earth
    centripetal force
  2. forward velocity
    Forces are balanced which causes the object to be held in orbit.
    continuously falling toward Earth
    It is accelerating because it is changing direction

7th grade year (7 decks)

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