Forces and speed - Free Printable

Here is the completed worksheet with explanations for each answer.

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Task 1

#### 1. Complete the table.

| Circle the contact forces. | magnetism | gravity | friction |
|----------------------------|-----------|---------|----------|
| | upthrust | | air resistance |

> Explanation: Contact forces are forces that act only when two objects are physically touching. Friction and air resistance are contact forces because they result from surfaces rubbing against each other (or an object moving through a fluid like air). Upthrust (buoyancy) is also a contact force — it’s the upward push of a fluid on an object submerged in it. Magnetism and gravity are non-contact forces — they act at a distance without physical contact.

✔ So, you should circle: friction, upthrust, air resistance.

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Now, answer the questions by selecting the correct force(s) from the column headers:

| Question | Answer |
|----------|--------|
| Which force always goes against moving objects? | friction |
| Which force causes objects to float in water? | upthrust |
| Which force slows down objects which are moving through the air? | air resistance |
| Which force causes objects to be pulled towards the ground? | gravity |

> Explanations:
> - Friction opposes motion between surfaces in contact — it always acts *against* the direction of movement.
> - Upthrust (or buoyant force) pushes objects upward in fluids (like water), allowing them to float if it balances their weight.
> - Air resistance is a type of friction that opposes motion through air — it slows down flying or falling objects.
> - Gravity pulls all objects with mass toward each other — on Earth, this means pulling things toward the ground.

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#### 2. Label the forces on the force diagrams below.

For the airplane:

- Upward arrow → Upthrust / Lift (The wings generate lift to counteract gravity)
- Downward arrow → Gravity (Pulls the plane down)
- Leftward arrow → Air resistance / Drag (Opposes forward motion)
- Rightward arrow → Thrust (Generated by engines to push the plane forward)

> ✔ Note: While “upthrust” is technically used for buoyancy in liquids, in aviation we usually say “lift.” However, since the worksheet uses “upthrust” as a column header, and it’s the upward force countering gravity, it’s acceptable here.

For the car:

- Upward arrow → *(Not shown — but implied normal reaction force from ground)*
- Downward arrow → Gravity
- Leftward arrow → Friction / Air resistance (This opposes motion — could be either, but since it’s a car on ground, friction is more accurate unless specified as air resistance. But the diagram shows a side view with arrows matching thrust/drag, so likely air resistance or drag.)
- Rightward arrow → Thrust / Driving force (From engine pushing car forward)

> ✔ Since the worksheet doesn’t specify “thrust” or “driving force,” and the keywords are limited to those in Task 1, you can label:
> - Right arrow: (Driving force — not listed, so perhaps leave blank or note “thrust”)
> - Left arrow: friction (if rolling friction) or air resistance (if aerodynamic drag). Given the context, air resistance is most appropriate for a car moving forward.

> ⚠️ Important: The worksheet does not include “thrust” or “driving force” as options, so for accuracy, you might need to infer. In many school contexts, for cars, the forward force is called “driving force” and backward is “friction/air resistance.” Since “air resistance” is in the table, and the car is moving, left arrow = air resistance, right arrow = driving force (though not listed). If forced to use only words from the table, you may have to write “not applicable” or note the limitation.

> Suggested labels using available terms:
> - Plane:
> - Up: upthrust
> - Down: gravity
> - Left: air resistance
> - Right: *(No direct term — perhaps “thrust” is implied, but not listed)*
> - Car:
> - Down: gravity
> - Left: friction (or air resistance)
> - Right: *(No term — driving force not listed)*

> 📝 Recommendation for students: Use “upthrust,” “gravity,” “air resistance,” and “friction” where possible. For the rightward forces, if allowed, write “thrust” or “driving force” even if not in the table, as it’s essential for understanding.

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#### 3. Fill in the blanks using the words below.

Keywords: direction, speed, same, balanced, unbalanced

> Completed sentences:

> If the forces on an object are balanced, the object will be stationary or stay moving at the same speed.

> If the forces on an object are unbalanced, the object will change speed, shape or direction.

> In the diagram the forces on the plane are balanced, therefore its speed is not changing. But the forces on the car are unbalanced, therefore the car’s speed is changing.

> ✔ Explanation:
> - When forces are balanced, the net force is zero → no acceleration → object remains at rest or moves at constant speed in a straight line (Newton’s First Law).
> - When forces are unbalanced, there is a net force → acceleration occurs → speed or direction changes (or both).
> - In the plane diagram, if all arrows are equal length (implied), forces are balanced → constant speed.
> - In the car diagram, if the forward arrow is longer than the backward arrow (common depiction), forces are unbalanced → car accelerates (speed changes).

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✔ Final Answers Summary:

#### Task 1.1 Table:
- Circle: friction, upthrust, air resistance
- Against moving objects: friction
- Float in water: upthrust
- Slows in air: air resistance
- Pulled to ground: gravity

#### Task 1.2 Force Diagrams:
- Airplane:
- Up: upthrust
- Down: gravity
- Left: air resistance
- Right: *(thrust — not listed; if must use table, perhaps omit or note)*
- Car:
- Down: gravity
- Left: friction (or air resistance)
- Right: *(driving force — not listed)*

#### Task 1.3 Fill-in-the-blanks:
1. balanced, same, speed
2. unbalanced, speed, direction
3. balanced, speed, unbalanced

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Let me know if you’d like a printable version or visual annotations!