C9 | 힘의 적용과 에너지 전달 (Application of Forces & Transfer of Energy)

Question 1

What is Force?

Hint: How is it produced? General Definition?

Answer 1

• A force can be a push or a pull.
• A force is produced by touching an object with our body,
  or by touching it with another object.
• Forces can also act when objects do not touch.

Question 2

What are the different types of Forces?

Answer 2

• Contact Force
• Non-Contact Force

Question 3

What is Friction?

Answer 3

The contact force that acts on two materials rubbing against each other is called Friction.

Question 4

What is a Contact Force?

Answer 4

• Whenever an object is touched, contact forces act on it.
• For example, the tyres of a car rest on the road and exert a contact force on the road.

Question 5

What is a Non-Contact Force?

Answer 5

• A force that acts on an object without touching it is called a non-contact force.
• Gravitational force, electrostatic force and magnetic force
  are examples of non-contact forces.

Question 6

What is the force that the Earth exerts on objects?

Answer 6

Weight
As weight is a force, the SI Unit is N

Question 7

What is the instrument used to measure Force?
There are two types, they are?

Answer 7

Spring Balance
* The spring in an extension spring balance stretches when a pulling
force acts on it. (Put something on the hook and it falls, to measure.)
* The spring in a compression spring balance compresses when a pushing force acts on it. (Like standing on a Weighing Scale.)

Question 8

What is Mass?

Answer 8

The amount of matter contained in an object.
* The force of gravity (weight) is different on different massive
objects, e.g. planets. The weight of a person on the earth is
greater than his weight on the moon. This is due to the stronger
gravity on the earth.

9.81 m/s2 (Earth’s Gravity), 1.62 m/s2 (Moon’s Gravity)

Question 9

If you weight 60kg and 600N on Earth, how much do you weight on the Moon?

Answer 9

60 Kilograms
100 Newtons

Question 10

What is Pressure?

Answer 10

• Pressure is the amount of force acting perpendicularly on a unit area.
• Pressure is an effect of a force acting on an object.

Question 11

How do you calculate Pressure?

Answer 11

• Pressure can be calculated by measuring the amount of force applied on a surface and the area of the surface.
  Pressure = Force/Area
  (FAP Triangle)
• The SI unit of Pressure is Pascals. (Pa)
• The unit of pressure is newton per square metre. (N/m2)

Question 12

수학 문제

A lady weighing 450 N stands on one stiletto heel of area
0.0001 m2

What pressure is exerted on the ground?

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Answer 12

Pressure = Force/Area
= 450N/0.0001m2
= 4 500 000 N/m2

Question 13

What is work done?

Answer 13

Work Done is the ability to do work.
* The SI unit of energy and work done is the Joule (J).
* One joule of energy is needed to do one joule of work.

Question 14

What are the prerequisites for work to be done?

Answer 14

1. A force is applied on the object.
2. The object moves.
3. The object moves in the same direction as the force applied on it.

Question 15

Marie is rearranging equipment in a room. She picks up a box from the
floor and places it on a high shelf.

Marie applies a force of 40 N on the box. The shelf is 2 m above the floor.

Is there work done?

Answer 15

• There is work done on the box because a force of 40 N is applied to move the box over a distance of 2 m.
• The box moves in the same direction in which the force was exerted.

Question 16

After rearranging the equipment, Marie holds a basket of tennis balls and stands for a while without moving.

Marie applies a force of 50 N on the basket. She holds the basket 1m above the floor.

Is there work done?

Answer 16

No work is done on the basket. A force of 50 N is exerted on the basket. However, the basket does not move in the same direction as the force exerted (it remained stationary).

Question 17

Marie carries the basket of tennis balls out of the room. She walks a distance of 20 m on level ground along a corridor.

She applies an upward force of 50 N on the basket. As she walks, Marie carries the basket at the same height above the ground.

Is there work done?

Answer 17

No work is done on the basket. A force of 50 N is exerted on the basket, which moves over a distance.

However, the distance moved by the basket is not in the same direction as the force exerted on the basket. (Upward Force as the basket is being carried, but moving in a straight line)