Forces

Question 1

What is force?

Answer 1

Push or pull upon an object’s interaction with another object. Forces have both size and direction.

Question 2

What is a contact force?

Answer 2

When two interacting forces are perceived to be physically contacting.

Question 3

What is action-at-a-distance forces?

Answer 3

Result when two interacting objects are not in physical contact with each other, yet are able to exert a push or pull despite their physical seperation.

Question 4

What is an unbalanced force?

Answer 4

Cause a force to stop moving, start moving, or change direction (Causes acceleration) non zero net force.

Question 5

What is a balanced force?

Answer 5

Equal forces acting on one object in opposite directions (Does not change the current state of motion. Might not move or move at constant spped)

Question 6

What is net force?

Answer 6

Overall (sum) force acting on an object

• Forces that act in the same direction (+)
• Forces that act in opposite directions (-)

Question 7

Net force problems:
10N + 5N + 13N =
–> –>. –>

Answer 7

28N

—>

Question 8

7N + 2N + 8N =

–>.

Answer 8

13N

–>

Question 9

What is friction?

Answer 9

Force one surface exerts on another when the surfaces rub against each other. (When 2 surfaces rub together the irregularities of one surface get caught on those of another)

Friction is an unbalanced force that opposes motion.

Question 10

What does the strength of friction depend on?

Answer 10

The type of surfaces involved and how hard the surfaces push together.

Question 11

What type of force is friction?

Answer 11

Unbalanced force that opposes motion

Question 12

What are the types of friction?

Answer 12

Static friction: Fictional resistance a stationary object must overcome to be set in motion

Kinetic friction (What happens after you overcome static):

• Sliding friction: When solid forces slide over each other
• Rolling friction: When an object rolls over a surface (like bowling)
• Fluid friction: When an object moves through liquid or gas

Question 13

What is gravity?

Answer 13

Attractive force which pulls two objects towards each other. The strength of the gravitational force between the two objects depends on two factors; mass and distance.

Question 14

Notes: More mass = more gravitational pull
Distance: Closer = stronger gravitational pull

Answer 14

Notes: More mass = more gravitational pull
Distance: Closer = stronger gravitational pull

Question 15

Two students are sitting 1.5 m apart. One has 70.0 kg mass and other has 52 kg mass. What is the gravitational force?
(Formula: F = G(m1*m2/r^2)
G = 6.67 * 10^-11
r = distance

Answer 15

Answer: 0.00000108 or 1.08*10^-7 N

Question 16

Note: It is not the original forces that determines the acceleration of an object, it is the Net Force that determines the motion.

Answer 16

Note: It is not the original forces that determines the acceleration of an object, it is the Net Force that determines the motion.

Question 17

How fast will an object accelerate if the net force is 0?

Answer 17

The object will not accelerate, the force acting on it will be balanced but it will not move.

Question 18

A skydiver dives downward?

Balanced or unbalanced

Answer 18

Unbalanced

Question 19

A motorbike moving at a constant speed in a straight line?

Balanced / Unbalanced

Answer 19

Balanced

Question 20

A bike leans against a tree

Balanced / Unbalanced

Answer 20

Balanced

Question 21

One team wins a tug-of-war-against another?

Balanced / Unbalanced

Answer 21

Unbalanced

Question 22

The parking brake is on the car?

Balanced / Unbalanced

Answer 22

Balanced

Question 23

A marble accelerates down a ramp?

Balanced / Unbalanced

Answer 23

Unbalanced

Question 24

What is Newton’s Law of Universal Gravitation?

Answer 24

The force of gravity acts on all objects of the universe; exists between all objects in the universe; attractive force exists between any and all objects in the universe

Question 25

Two bricks are left motionless in outer space with nothing around them. Will there be any gravitational attraction between them?

Answer 25

Yes, according to Newton's law of universal gravitation.

Question 26

``` Are you (scientifically) attracted to a mountain 3km away? Why are you/why are you not pulled towards the mountain? ```

Answer 26

Yes, cause of Newton's law of Universal Gravitation. The force of gravity between us and the earth is much greater than the force of gravity between us and the mountain.

Question 27

What is gravity?

Answer 27

Attractive force which pulls two objects towards each other.

Question 28

What is free-fall?

Answer 28

Any object that is being acted upon only by a force of gravity is said to be in a state of free-fall. - Free-falling objects do not encounter air resistance - All free-falling objects (on Earth) accelerate downwards at a rate of 9.8m/s/s

Question 29

What is air resistance?

Answer 29

Fluid friction (opposite to motion) resulting from collisions between the object's leading surface and air molecules. The amount of air resistance depends on: - Speed of object - Amount of air resistance

Question 30

What does air resistance depend on?

Answer 30

- Speed of object | - Amount of air resistance

Question 31

That is terminal velocity?

Answer 31

Moment at which air resistance equals the force of gravity. Object reaches its greatest velocity.

Question 32

What is a projectile?

Answer 32

Object upon which the only force acting is gravity

Question 33

What is projectile motion?

Answer 33

Motion associated with the projectile

Question 34

What is trajectory?

Answer 34

The path followed by a projectile (directly influenced by gravity) - Gravity only causes vertical acceleration

Question 35

A boy drops a rock into a pond. At the same time his friend drops a rock twice as large. Ignoring air resistance will his friends rock: A. Reach the water first B. Reach the water last C. Reach the water at the same time

Answer 35

C. Reach the water at the same time

Question 36

A skydiver jumps out of an airplane and begins to freely fall to the ground. As he pulls out his camera to take a picture he accidentally lets it go. Ignoring air resistance the camera will: A. Fall at the same rate as the skydiver B. Fall slower than the skydiver C. Fall faster than the skydiver

Answer 36

A. Fall at the same rate as the skydiver

Question 37

All free-falling objects accelerate (on Earth) at a rate of _____

Answer 37

9.8 m/s/s

Question 38

An object in free-fall covers ____ distances every second

Answer 38

unequal

Question 39

When the skydiver jumps from the airplane gravity acts as an unbalanced force causing the skydiver to accelerate downwards. The faster the skydiver falls, the greater the air resistance acting against until the two forces become equal and balanced. Here the skydiver has reached terminal velocity. They do not stop falling, they simply stop accelerating or falling any faster than they once were. We see this at 55m/s. Once the sky diver deploys their parachute what does this do to their new “safer” terminal velocity?

Answer 39

Terminal velocity decreases

Question 40

Note: How to tell if a graph is free-fall - The height vs time is a curve because an object in free-fall covers unequal distances. - The acceleration vs time would be around 9.8. Which is the rate that an object accelerates in free-fall. - Velocity vs time is steady

Answer 40

Note: How to tell if a graph is free-fall - The height vs time is a curve because an object in free-fall covers unequal distances. - The acceleration vs time would be around 9.8. Which is the rate that an object accelerates in free-fall. - Velocity vs time is steady

Question 41

Note: If an acceleration vs time graph curves and hits the 0 line at, lets say x = 1, that means that the object reached terminal velocity at 1.

Answer 41

Note: If an acceleration vs time graph curves and hits the 0 line at, lets say x = 1, that means that the object reached terminal velocity at 1.

Question 42

When Apollo 15 astronaut David Scott did his famous freefall experiment on the Moon, he dropped a falcon feather from a height of about 1.6 meters. Assuming a gravitational acceleration of 1.6 m/s/s on the Moon, about how long did it take the feather to drop to the surface? Remember time = √(2d/a)

Answer 42

2 seconds

Question 43

A boy finds an abandoned mine shaft in the woods, and wants to know how deep the hole is. He drops in a stone, and counts 4 seconds before he hears the "plunk" of the stone hitting the bottom of the shaft. Approximately how deep is the shaft? (Assume a gravitational acceleration of 9.8 m/s/s and no air resistance.) Remember distance = ½ at2

Answer 43

78 m

Question 44

A boy finds an abandoned mine shaft in the woods, and wants to know how deep the hole is. He drops in a stone, and counts 4 seconds before he hears the "plunk" of the stone hitting the bottom of the shaft. Approximately how deep is the shaft? (Assume a gravitational acceleration of 9.8 m/s/s and no air resistance.) Remember distance = ½ at2

Answer 44

78 m

Question 45

A squirrel drops a nut over a cliff. Calculate the velocity of the nut after 3 seconds. (Assume a gravitational acceleration of 9.8 m/s/s and no air resistance.) Remember velocity = at

Answer 45

29.4

Question 46

Newton’s 1st Law of Motion

Answer 46

Objects at rest stay at rest and objects in motion stay in motion at a constant velocity unless an unbalanced force acts on it to make it accelerate.

Question 47

Ellen is hammering a chisel into a block of marble to carve a sculpture. The hammer is pushing the chisel forward with a force of 40N. The block of marble is pushing the chisel backward with a force of 40N. Assume all other forces on the chisel are balanced. Which statement describes the forces on the chisel?

Answer 47

The forces are balanced, so there is no net force on the chisel.

Question 48

Tammy is walking her dog, Ruby. A squirrel just ran by, and Ruby is pulling forward on the leash with a force of 250N. Tammy is pulling backward on the leash with a force of 180N. Assume all other forces on the leash are balanced. Which statement describes the forces on the leash?

Answer 48

The forces are unbalanced, so there is a net force on the leash.

Question 49

Sandra is sitting on a porch swing while her young son sits in her lap. Earth's gravity is pulling down on Sandra with a force of 800N. Sandra's son is pushing down on her with a force of 300N. The swing is pushing up on Sandra with a force of 1,100N. Assume all other forces on Sandra are balanced. Which statement describes the forces on Sandra?

Answer 49

The forces are balanced, so there is no net force on Sandra.

Question 50

Inertia

Answer 50

Resistance an object has to a change in motion

Question 51

Pete Zaria is being chased through the open woodlands by an African Lion which he was attempting to photograph. The enormous mass of the lion is extremely intimidating! However, if Pete utilizes Newton's first law of motion (inertia) and runs in a particular direction he will be able to use the large mass of the lion to his own advantage and escape! Which direction should Pete run?

Answer 51

Zigzag

Question 52

“Although weight is reduced in outer space, the mass of an object is unchanged, to move a (stationary) mass force must be applied” This statement describes Newton's

Answer 52

First Law of Motion

Question 53

``` A rocket will accelerate A. By pushing against Earth's surface B. By pushing against Earth's atmosphere C. In outer space (a vacuum) D. A,B,C E. A,B F. B,C G. A, C ```

Answer 53

C

Question 54

The male skater pushes against the female skater (action force). The result is the female skater pushing back against the male skater with an equal force (reaction force). Which of Newton's laws describes this phenomenon?

Answer 54

Newton's Third law of motion

Question 55

Assuming you are driving a car on the road, consider the motion of the car. As the wheels of the car spin backwards, they push the road backwards (action force). In consequence, the reaction force must be

Answer 55

The road pushing wheels foward

Question 56

While driving down the road, a bug strikes the windshield of the car pictured above and makes quite a mess. This scenario explains Newton's third law of motion. The bug hits the windshield and applies a force and the windshield hits the bug and applies a force. Which of the two forces is greater: the force on the bug or the force on the windshield?

Answer 56

The two forces are equal

Question 57

If "Action - Reaction" forces are always equal in strength and opposite in direction, how is it possible for an object to accelerate? Meaning, why don't these forces cancel each other?

Answer 57

Forces are acting on different objects

Question 58

If your skater has a mass of 68 kg and is at a height of 2 meters, calculate their potential energy. PEgrav = mass * 9.8 m/s/s * height

Answer 58

1332.8 joules

Question 59

If your skater has a mass of 68 kg and a velocity of 5 m/s, calculate their kinetic energy. KE = 1/2(mass * velocity^2)

Answer 59

850 joules

Question 60

If your skater has a mass of 68 kg and is now at the height of 4 meters, calculate their potential energy. PEgrav = mass * 9.8 m/s/s * height

Answer 60

2665.6 joules