forces and motion – student worksheet
1. define a force.
2. list two effects of forces.
3. draw a force diagram showing gravity, normal force, and friction.
4. is a book on a table balanced or unbalanced? explain.
5. calculate net force: 20 n right, 10 n left.

Question

Accepted Answer

### Question 1: Define a force.
# Brief Explanations:
A force is a push or pull on an object resulting from its interaction with another object. Forces can cause changes in an object's motion (like starting, stopping, or changing direction) or in its shape. In physics, force is a vector quantity, meaning it has both magnitude (size) and direction, and is measured in newtons (N).
# Answer:
A force is a push or pull acting on an object, arising from its interaction with another object, capable of causing changes in the object’s motion (e.g., accelerating, decelerating, changing direction) or shape; it is a vector quantity (with magnitude and direction) measured in newtons (N).

### Question 2: List two effects of forces.
# Brief Explanations:
Forces can alter an object's state of motion. For example, a force can make a stationary object start moving (like pushing a stationary cart) or make a moving object stop (like applying brakes to a car). Additionally, forces can change the shape of an object, such as compressing a spring or stretching a rubber band.
# Answer:
1. Forces can change an object’s state of motion: e.g., a force can cause a stationary object to start moving (e.g., pushing a stationary box) or a moving object to stop (e.g., braking a car).
2. Forces can change an object’s shape: e.g., compressing a spring or stretching a rubber band.

### Question 3: Draw a force diagram showing gravity, normal force, and friction.
# Brief Explanations:
To draw a force diagram (free - body diagram) for an object (e.g., a book sliding on a table or a box on an incline), follow these steps:
1. **Identify the object**: Let's take a book sliding on a horizontal table as an example.
2. **Gravity (Weight)**: Draw a downward - pointing arrow from the center of the object, labeled $ F_g $ (or $ W $) to represent the force of gravity pulling the object towards the Earth.
3. **Normal Force**: Draw an upward - pointing arrow from the bottom of the object (where it contacts the table), labeled $ F_N $ (or $ N $). This force is perpendicular to the surface (for a horizontal table, it is vertical) and is exerted by the table to support the object, balancing the force of gravity in the vertical direction (if the object is on a horizontal surface and not accelerating vertically).
4. **Friction**: If the object is moving (or has a tendency to move) relative to the surface, draw a frictional force arrow. For a book sliding to the right on the table, the kinetic friction force $ F_f $ (or $ f $) acts to the left (opposing the motion), parallel to the surface.

For an object on an inclined plane:
- Gravity still acts downward from the center.
- The normal force acts perpendicular to the incline (not vertical).
- Friction (if present) acts parallel to the incline, opposing the motion (or tendency to move) of the object.

The diagram should have the object represented as a simple shape (like a rectangle), with arrows for each force labeled clearly.
# Answer:
To draw the force diagram (using a book sliding on a horizontal table as an example):

1. **Represent the object**: Draw a rectangle (to represent the book) at the center of your diagram.
2. **Gravity ($ \boldsymbol{F_g} $)**: Draw a downward - pointing arrow from the center of the rectangle, labeled $ F_g $ (or $ W $), to show the force of gravity pulling the book toward the Earth.
3. **Normal Force ($ \boldsymbol{F_N} $)**: Draw an upward - pointing arrow from the bottom edge of the rectangle (where it touches the table), labeled $ F_N $ (or $ N $), perpendicular to the table’s surface (vertical, for a horizontal table) to show the table’s upward support force.
4. **Friction ($ \boldsymbol{F_f} $)**: If the book is sliding (e.g., to the right), draw a left - pointing arrow parallel to the table’s surface, labeled $ F_f $ (or $ f $), to show the kinetic friction opposing the book’s motion.

### Question 4: Is a book on a table balanced or unbalanced? Explain.
# Brief Explanations:
A book on a table is in a state of balanced forces. In the vertical direction, the force of gravity (pulling the book downwards) and the normal force (exerted by the table, pushing the book upwards) act on the book. These two forces are equal in magnitude and opposite in direction. According to Newton's first law of motion, when the net force (the vector sum of all forces) acting on an object is zero, the object is in a state of equilibrium (either at rest or moving with a constant velocity). Since the book is at rest on the table, and the vertical forces (gravity and normal force) cancel each other out (there are no horizontal forces acting on a stationary book on a table in the absence of external pushes or pulls), the net force on the book is zero.
# Answer:
A book on a table is **balanced**.

Explanation: The book experiences two main vertical forces:
- **Gravity ($ F_g $)**: Pulls the book downward toward the Earth.
- **Normal Force ($ F_N $)**: Pushes the book upward, exerted by the table (perpendicular to the table’s surface).

These two forces are equal in magnitude ( $ F_N = F_g $) and opposite in direction (gravity down, normal force up). Since there are no horizontal forces (or they are balanced, too, for a stationary book), the **net force** (vector sum of all forces) on the book is $ 0 $. By Newton’s first law, an object with a net force of $ 0 $ is in equilibrium (balanced), so the book remains at rest.

### Question 5: Calculate net force: 20 N right, 10 N left.
# Explanation:
## Step 1: Define the direction of forces
Let's take the right - hand direction as positive and the left - hand direction as negative. So, the force to the right ($ F_1 $) is $ + 20\space N $ and the force to the left ($ F_2 $) is $ - 10\space N $.

## Step 2: Calculate the net force
The net force ($ F_{net} $) is the sum of all the forces acting on the object. So, $ F_{net}=F_1 + F_2 $. Substituting the values of $ F_1 $ and $ F_2 $, we get $ F_{net}=20\space N+( - 10\space N) $.

## Step 3: Simplify the expression
$ 20\space N- 10\space N = 10\space N $. The positive sign indicates that the net force is in the right - hand direction.
# Answer:
The net force is $ 10\space N $ to the right.

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Question

Explanation:

Question 1: Define a force.

Answer:

Question 2: List two effects of forces.