Although the motion that results from the forces at work in the world are observable, the forces themselves are abstract and invisible, making it hard to explain in concrete terms for young children. Introduce examples of how gravity and friction push and pull on objects to start and stop motion by reading books such as, "Push and Pull" by Patricia J. Murphy, "Force Makes Things Move" by Kimberly Bradley or "And Everyone Shouted, 'Pull!'" by Claire Llewellyn.
Children often don't notice or stop to think about how many simple tasks they take for granted are made possible because of pushes and pulls. Give the children a chart with columns for "push," "pull" and "both" and a pad of sticky notes. Let them explore the room or the school for examples of objects that move by pushing or pulling. For example, doors, light switches, drawers, the custodian's cart or the swings. For more examples, assign the chart as homework and have children look for additional items at home such as the brake and accelerator in the car, the buttons on the phone, TV or video game system, the computer keyboard, toys and bicycles.
Children may easily grasp that force makes things move but you can stretch them still further by demonstrating that the force necessary to produce motion changes with the mass or weight of the object to be moved. To demonstrate pulling forces, loop a rubber band around a toy dump truck's bumper and place the truck at the end of a yardstick. Pull on the rubber band and note the distance it stretches before the truck moves. Add weight to the back of the truck and try it again. Compare the force needed to move the loaded truck versus the empty truck and draw a conclusion about how weight affects force and motion. To demonstrate pushing forces, place the toy truck at the end of an inclined plane. Roll a large marble or rubber ball down the ramp and measure how far the truck moves when pushed by the rolling sphere. Try changing the weight of the truck or the height of the ramp or size of the ball to determine the relationship between force and weight.
Simple machines such as the inclined plane, lever and pulley make it easier to push or pull heavy loads. Set a heavy box on a desk or table and show how difficult it is to lift it to the floor. Set a piece of plywood against the table and demonstrate how much easier it is to just slide the box down the ramp. Ask a child to try to pick you up. After demonstrating that he cannot accomplish this task under his own power, tell the children that they can easily pick you up with a simple machine called a lever. Take the class out to the playground and sit on one end of the teeter totter. Have one or more children sit on the other end until they succeed in lifting you by pushing down on their end. Challenge students to think of their own uses for simple machines and build a simple model to demonstrate the pushing and pulling forces at work in machines.