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Flashcards in science force and motion Deck (45)
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1

state the law of universal gravitation

the force of gravity acts between all objects in the universe

2

what is weight

a measure of gravitational pull, measured in Newtons

3

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

weight changes with location
mass doesn't change

4

What two factors affect the strength of gravity?

mass and distance

5

How do mass and distance affect gravitational pull?

more mass = more gravitational pull
the farther apart, the less the gravitational pull

6

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

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

7

Explain static friction.

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

8

Give an example of static friction.

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

9

Explain sliding friction.

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

10

Give an example of sliding friction.

throwing sand on ice to get friction for walking or driving

11

Explain fluid friction.

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

12

Give an example of fluid friction.

water on a water slide
oil on a squeaky hinge

13

Explain rolling friction.

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

14

Give an example of rolling friction.

wheels or ball bearings

15

How is force described?

by its strength and direction

16

What is a net force?

a combination of all forces acting on an object

17

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

subtract

18

Define Newton's 1st Law of Motion.

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

19

Define Newton's 2nd Law of Motion.

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

20

Define Newton's 3rd Law of Motion.

For every action there is an equal and opposite reaction.

21

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

You have to have unbalanced force to cause motion.

22

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

force

mass acceleration

23

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

9.8m/s or 32 feet/s

24

What is the SI unit for acceleration?

m/s meters/second

25

What is the SI unit for force?

N (newtons)

26

What is the SI unit for mass

kilogram kg

27

What two factors affect the force of friction?

types of surfaces involved
how hard the surfaces are pressed together

28

Identify one product of friction.

heat
wears surfaces down
slows movement

29

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.

35N + 60N = 95 N

95N - 20N = 75N of net force

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

30

Identify the action-reaction forces involved in walking.

action - foot pushes down and back on the ground
reaction - the ground pushes your foot up and forward