"The Force from the Earth" Familiar and Unfamiliar Forces PPT Courseware 4

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"The Force from the Earth" Familiar and Unfamiliar Forces PPT Courseware 4

Observe and think:

1: Release a heavy object freely

2: Throw an object horizontally

3: Observe a picture of water flowing downwards

Phenomenon Why does the following phenomenon occur?

1: The heavy object falls vertically,

2: The thrown object falls back to the ground,

3: The waterfall flows from high to low.

in conclusion:

1: It turns out that all objects near the surface of the earth are attracted by the earth.

2: In physics, the force exerted by an object due to the attraction of the earth is called gravity.

Thinking: How to understand gravity?

Gravity is the attraction of the earth to objects. Therefore, the object exerting force by gravity is the earth, and the object receiving force is all objects near the surface of the earth.

In physics, the amount of gravity exerted by an object is also called its weight.

Observe and think:

1: What do masons use to check whether a wall is straight?

2: What do masons use to check whether the window sill is level? Is the door frame placed correctly?

3: How do we check whether the paintings on the wall are hung correctly?

Conclusion: Use heavy vertical lines

Because when a heavy object is hung under a line, after the weight is stationary, under the action of gravity, the direction of the hanging line is consistent with the direction of gravity.

Thinking: What is the direction of the hanging line? What is the direction of gravity?

The direction of gravity is vertically downward.

Consolidation exercises:

1: What forces act on an ink bottle placed on a horizontal table? What are the force-exerting objects?

2: As shown in the figure below, an object weighing 32N is placed on an inclined plane, and the force diagram represents the gravity exerted on it.

3: As shown in the picture, you can see the weight limit sign as shown in the picture on the bridge head (t means tons). It indicates how many oxen is the heaviest car allowed to pass on this bridge?

4: There is an object with a weight of 39.2N. Can I use a scale with a maximum weighing capacity of 500g to determine its mass?

It is known that the mass of the cars allowed to pass through this bridge is m=30t=30000kg

The gravity constant is g=9.8N/kg

Find: G the gravity of the cars allowed to pass through this bridge

Solution: From G=mg=30000kg×9.8N/kg=294000N= 2.94×105N

Answer: The gravity of the cars allowed to pass through this bridge is 2.94 × 105N

Known: The gravity of this object is G=39.2N

The gravity constant is g=9.8N/kg

Find: the mass m of this object. Then compare it with the maximum weighing capacity of the balance, 500g.

Solution: From m=G/g=39.2N/9.8N/kg=4kg=4000g>500g

Therefore, this object cannot be weighed on a balance with a maximum weighing capacity of 500g.

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Update Time: 2024-07-30

This template belongs to Physics courseware Shanghai Science Edition 8th Grade Physics industry PPT template

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