Circle the pictures that show an example of a force.

Problem Description:

The task is to identify and circle the pictures that show an example of a force. The concept of "force" in physics refers to a push, pull, or any interaction that can change the motion or shape of an object.

Solution Approach:

1. Understand the Concept of Force:
- A force is any interaction that causes a change in the motion or shape of an object.
- Examples include pushing, pulling, gravity, friction, etc.

2. Analyze Each Picture:
- Carefully examine each image to determine if it depicts a situation where a force is being applied or observed.

3. Identify Forces:
- Look for actions such as pushing, pulling, falling, hitting, or any other interaction that involves a change in motion or shape.

4. Circle the Relevant Pictures:
- Mark the images that clearly demonstrate the presence of a force.

---

Analysis of Each Image:

#### Top Row:
1. Car Hitting a Hill:
- The car is colliding with the hill, which indicates a force (impact force) acting on both the car and the hill.
- Force is present.

2. Sofa with Pillows:
- The sofa and pillows are stationary, and there is no visible interaction or change in motion or shape.
- No force is present.

#### Middle Row:
3. Fox Eating from a Bowl:
- The fox is eating, but there is no indication of a force being applied to the bowl or the food.
- No force is present.

4. Child Pulling a Tree Branch:
- The child is actively pulling the tree branch, which demonstrates a force being applied to the branch.
- Force is present.

5. Sunflower Growing:
- The sunflower is growing, but this is a natural process and does not involve a force being applied by an external agent.
- No force is present.

#### Bottom Row:
6. Rock Falling Down a Ramp:
- The rock is falling down the ramp due to gravity, which is a force.
- Force is present.

7. Girl Playing Tennis:
- The girl is hitting the tennis ball with a racket, which involves a force being applied to the ball.
- Force is present.

---

Final Answer:

The images that show examples of force are:
1. Car hitting a hill
2. Child pulling a tree branch
3. Rock falling down a ramp
4. Girl playing tennis

Circled Images:
- Top row: 1st image
- Middle row: 2nd image
- Bottom row: 1st and 2nd images

Final Answer Boxed:
\boxed{1, 4, 6, 7}