Educational worksheet on buoyancy and floating objects, designed for classroom science activities.

Problem Overview:

The task involves understanding how objects float or sink in water based on their weight and the force of gravity acting on them. The key concept here is buoyancy, which is the upward force exerted by a fluid (like water) on an object submerged in it.

#### Key Points from the Background Knowledge:
1. Buoyant Force: When an object is placed in water, the water pushes up on the object with a buoyant force.
2. Gravity: The force of gravity pulls the object downward.
3. Floating Condition: For an object to float, the buoyant force must be greater than the force of gravity (weight of the object).

#### Given Data:
The table provides the weights of different objects in air and in water:
| Object | Weight in air (N) | Weight in water (N) |
|---------------|-------------------|---------------------|
| Wooden block | 20 N | 0 N |
| Glass marble | 50 N | 40 N |
| Plastic spoon | 50 N | 0 N |

#### Task:
Use the table above to determine which objects will float. Explain your reasoning.

---

Solution:

#### Step 1: Understand the principle of floating
An object floats if the buoyant force is greater than or equal to the weight of the object (force due to gravity). Mathematically:
- Buoyant force = Weight of the object in air - Weight of the object in water
- If buoyant force > weight of the object, the object will float.
- If buoyant force < weight of the object, the object will sink.

#### Step 2: Calculate the buoyant force for each object
We use the formula:
\[
\text{Buoyant force} = \text{Weight in air} - \text{Weight in water}
\]

##### Wooden block:
- Weight in air = 20 N
- Weight in water = 0 N
\[
\text{Buoyant force} = 20 \, \text{N} - 0 \, \text{N} = 20 \, \text{N}
\]
Since the buoyant force (20 N) is equal to the weight of the wooden block (20 N), the wooden block will float.

##### Glass marble:
- Weight in air = 50 N
- Weight in water = 40 N
\[
\text{Buoyant force} = 50 \, \text{N} - 40 \, \text{N} = 10 \, \text{N}
\]
Since the buoyant force (10 N) is less than the weight of the glass marble (50 N), the glass marble will sink.

##### Plastic spoon:
- Weight in air = 50 N
- Weight in water = 0 N
\[
\text{Buoyant force} = 50 \, \text{N} - 0 \, \text{N} = 50 \, \text{N}
\]
Since the buoyant force (50 N) is equal to the weight of the plastic spoon (50 N), the plastic spoon will float.

#### Step 3: Determine which objects float
From the calculations:
- Wooden block: Floats
- Glass marble: Sinks
- Plastic spoon: Floats

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Final Answer:

\[
\boxed{\text{Wooden block and Plastic spoon}}
\]

Explanation:

- The wooden block and plastic spoon have buoyant forces equal to their weights, so they float.
- The glass marble has a buoyant force less than its weight, so it sinks.