What do they look like? Tree swallows are small birds (about 14 cm long) with long wings and small legs and feet. They are irridescent greenish-blue on their head, shoulders and back, and white their chin, breast and belly. Tree swallows have a short black beak and dark brownish feet.
Ernest Rutherford concluded that an atom contains a very small, dense center, called a nucleus, with a positive charge as a result of his gold foil experiment.
A positively charged particle has great difficulty penetrating a target nucleus because the target nucleus has. 1. a positive charge, which repels the particle 3. the protection of surrounding electrons. 2. a negative charge, which attracts the particle 4. a very high binding energy. 6. In a fusion reaction, reacting nuclei must collide.